Ok, first things first: the dumpwallet problem: there are only 2 options that come to my mind:
1) are you entering the command in the correct window (help => debug window => console)
2) are you using a version prior to 0.9.0? (https://bitcoin.org/en/release/v0.9.0)

To answer the second question:
those letters and numbers are normal, it's probably the raw, signed transaction. Could you post or PM this signed transaction? It's not a security thread to do so, the signed transaction should have been broadcasted to the network to begin with (and in all fairness: the odds are really big that it actually was broadcasted at some point, the odds are just rather big that it was broadcasted so long ago that it is now forgotten by most nodes of the network)

The technical side of bitcoin can be a bit challenging for new members, don't worry about it

I'll try to answer your questions (i removed the lines that weren're really questions):


is it a transaction i tried to send from my QT wallet to another address in the past?
answer: your wallet thinks it controlls one of the unspent outputs generated by this transaction, it could be a transaction you yourself created, in that case it'll be funding a change address. It can also be a transaction generated by a thirth party funding one of your addresses.

i cannot work out what the private key is for that transaction
answer: a private key is used to sign a transaction, but that's not really important right now... What is importing is that you try to get your hands on the raw transaction, so we can examine it and, if possible, rebroadcast it...

if i do as bob123 says will i get all the private keys?
answer: yes

i don't quite understand this: dumpwallet "C:\path_to_your\output_file.txt"
answer: it's a command you should execute from the debug console... It'll create a textfile, in this case on your c-drive, in the folder path_to_your, the textfile will be named output_file.txt. The file will include (amongst other things) all private keys for all addresses ever generated (+100 pregenerated keys)

Sorry, but this answer is wrong on so many levels. I started correcting the post, but i had to give up, since after striking trough most of the errors, not much was left.

Basically, the newbie explanation of mining: a miner collects unconfirmed transactions, he verifies these transactions and he verifies all broadcasted blocks.
He then tries to combine these unconfirmed transactions into a block that has a maximum size of 1 Mb (disregarding the witness data, a block can be 4 Mb including the witness data). The first transaction in the block is the coinbase transaction, the coinbase transaction rewards the miner with 12.5 BTC and the sum of the fees of all transactions in the block. Every 210,000 blocks, the block reward of 12.5 BTC halves.

He then creates a merkle tree of the subset of transaction that forms his block

He then combines header information of the previous block, the merkle root, some other information and a nonce to form his new block's header. He then creates the sha256 hash of the sha256 hash of this header. If the outcome of the hash function is under the current target, his block is valid and he can broadcast his block.
If the outcome of the hashfunction is not under the current target, he increments the nonce and retries the hash function, just as long untill he finds a block header (including the nonce) whose outcome of the sha256d function is under target.

The difficulty makes sure that the target is so small that the average time between 2 blocks is 10 minutes. The difficulty gets adjusted every 2016 blocks.

@op:
The current difficulty is so high (and the target so low), it would take a massive amount of ASIC's to have a decent shot of finding a block header whose sha256d hash is under the current target, so people started forming pools. They pool their hashrate together to have a better shot at solving a block's header. Like other members already said: you joined a pool, you were pooling your hashrate together with other people... So when your pool found a block, you got rewarded a tiny piece of the total block reward.

So, your wallet thinks it has 2 unspent outputs available, but since it's not sync'ed, it thinks both of those transactions have 0 confirmations.

In reality, the first unspent output (coming from 62dc19dfe170b19f8d585b2cdfc68e6dd9f42261258089116c62b238404ab4e7, vout 0) is no longer known to most nodes. It was probably never confirmed, and probably got pruned from most node's mempool.

The second transaction was confirmed a while ago, and once your sync process is done, you should be able to spend this unconfirmed output.

Since it's vout 1, 1F6kQA5wFyx7uRxho3Xz3PMYRGhetdcjMt  should be the funded address belonging to your wallet. You could try to dump the private key for this address, or like bob123 already said: dump the whole wallet at once
BTW: if the problem forcing you to switch to an SPV wallet is space restrictions, i probably wouldn't sweep those addresses, just create a new wallet, and use the private keys to restore the wallet, that way, you won't have to spend BTC to pay the fees for the sweeping transaction (look at LoyceV's post for more info)

regarding the first unspent output, if i were you, i'd try to, i'd try to execute this command:
getrawtransaction 62dc19dfe170b19f8d585b2cdfc68e6dd9f42261258089116c62b238404ab4e7

Once you have the raw transaction, you should be able to rebroadcast it... However, there is a realistic chance the sender has re-used to unspent output used in this "forgotten" transaction to create a new transaction. If this new transaction confirmed, you've basically lost the unspent output.

Good luck!

Not only for a test... It's also possible an individual doesn't trust the person who compiled the binaries. In this case, the individual can pull bitcoin's source from github, effectively vet the sourcecode completely, then compile his own binaries, not for testing purposed, but for real live production usage.
As a matter of fact, i usually compile the binaries myself....

Is your wallet completely synced?
If it is, you can always try "listunspent 0", just to make sure you also include unconfirmed unspent inputs.

In theory, you're right... In case of a 80% drop 150.000 S9's will be sufficient... However, buying, setting up, running and maintaining 150.000 S9's is a collosal (and expensive) task. I mean, even after setting everything up, the power draw of such a mega farm would be enormous...

The price of 150.000 second hand antminers would still be over 10 million USD (my guesstimation), you'd need thousands of racks, you'd need special serverrooms with cooling, tech guys, cabling,... Just to be able to perform a 51% attack. A 51% in itself is also limited regarding the amount of history that can be rewritten. Even if you controll 51% of the hashrate, i don't think it would be wise to try to re-mine the last 10 blocks...
My point is: i think it would be pretty obvious who is executing a 51% attack if this person hash to spend multiple millions and dozens of tech guys to setup his infrastructure. I think that at this point, most people *might* have chosen the path of an altcoin that doesn't use sha256d as it's POW algo.
If word gets out that somebody untrustworthy might be preparing for a 51% attack, i guess most people will switch, lowering the bitcoin price, lowering the FIAT equivalent amount of BTC the attacker can effectively steal, making the whole endaveour even less profitable.

As for your second question: i don't know what will happen after all coinbase rewards are claimed. The theory is that bitcoin will be so valuable that miners will earn enough from mining fees. In reality, the reward halves every ~4 years anyways, so i think that sooner or later there'll be an equilibrium anyways. In my opinion, it won't take another 3 halvings before the income from collecting fees outweighs the income of the block reward anyways. Combine this with innovations on the ASIC front, changes in the protocol, regulation or deregulation, banning, changing electricity prices and it becomes completely impossible to make a prediction about the future of mining.

At this moment, the total hashrate is 19500 Ph/s.
In order to perform a 51% attack, you'd need a mining farm producing ~10.000 Ph/s, that's 10.000.000 Th/s

A single antminer S9 hashes at 14 Th/s.

So, you'd need about 700.000 S9's to perform a 51 attack right now.. The diff would have to drop a whole lot before a 51% attack is feasible.

That being said, your concern isn't completely unfunded... The theory is right. IF, for some reason, the hashrate drops steadily to (for example) 0.001% of the current hashrate, the diff would follow, and at that point, 7 S9's would suffice for a 51% attack. I do think that if this ever happens, there would be something seriously wrong, and a 51% will probably the least of our problems.

Well, to tell you the truth, as far as i can tell, electrum is correct: all unspent outputs funding that address HAVE been spent...

The address was funded with transaction 3fae9880f8a3dc9641a24114f5ab2fd502ae47a179478f5b360ee3c9156c1be1, but on 24/07/2013 the unspent output was spent in transaction 56e734f3f5df475f81469a339eb908e8f3e9f941f4ce36cf8d8febc6da24325c

https://blockchain.info/unspent?active=14G3Tr7PAb2L8xZKy2ib7MH9MscXHkQphj&format=html

So, if you try to sweep (or import) the private key belonging to 14G3Tr7PAb2L8xZKy2ib7MH9MscXHkQphj, it's logical electrum will give you an error...

GMX suddenly and without a warning or an explanation closed my email-account. Their support tools don't seem to work, and their support dept is only giving me scripted replies. I am forced to switch emails on my bitcointalk profile.

This post serves a dual purpose:
1) to proof my account wasn't sold, nor hacked (in case somebody is/was searching trough the seclog)
2) i lost all my contacts, and since 90% of them were aqcuired trough bitcointalk, it seemed like a good idear to post the address change on bitcointalk to notify my contacts.

-----BEGIN BITCOIN SIGNED MESSAGE-----
I am mocacinno from bitcointalk, ower of mocacinno.com. GMX closed my email on the 26th of januari 2018. I am forced to switch my email address. My past contacts can PM me on bitcointalk to receive my new email!
-----BEGIN SIGNATURE-----
1MocACiWLM8bYn8pCrYjy6uHq4U3CkxLaa
HA/4CQjIlg/8/LDi6rf6KIm2CNCHZYoDSHpeWd2SgeJ8HD7E6g9XCzJXWGB7goQibDgCpbzSMgHxWZNcapo3rEY=
-----END BITCOIN SIGNED MESSAGE-----

http://www.coinig.com/?adr=1MocACiWLM8bYn8pCrYjy6uHq4U3CkxLaa&msg=I+am+mocacinno+from+bitcointalk%2C+ower+of+mocacinno.com.+GMX+closed+my+email+on+the+26th+of+januari+2018.+I+am+forced+to+switch+my+email+address.+My+past+contacts+can+PM+me+on+bitcointalk+to+receive+my+new+email%21&sig=HA%2F4CQjIlg%2F8%2FLDi6rf6KIm2CNCHZYoDSHpeWd2SgeJ8HD7E6g9XCzJXWGB7goQibDgCpbzSMgHxWZNcapo3rEY%3D

The address was staked from this account allmost 2 years ago: https://bitcointalk.org/index.php?topic=996318.msg13770983#msg13770983

Like i said in the signed message: if any of my old contacts need my new email address, just PM me

If it's the seed of your HD wallet, you should be able to either restore your wallet in an other compatible HD wallet, or you should be able to derive the private keys... However, a lot of times new members get confused, and they think they have a seed for an HD wallet while in reality they have something completely different.

Could you tell us which wallet you were using and how many words are in the seed?

No problem
Do realise that this is a seriously flawed explanation i dumbed down to give a basic idear of what the lightning network is... I even had to correct a mistake i made during the creation of the post.

I myself only started experimenting with the lightning network for less than 2 weeks, i don't know all the in's and out's yet either, but i'm slowly gaining knowledge.

If you want to experiment, setting up a lightning network node is really easy... Just get yourself a small linux VPS (or install linux on your pc), install a bitcoin core deamon, sync it with the testnet, then compile https://github.com/ElementsProject/lightning and follow their very basic how-to tutorial... It took me about 2 hours to set everything up (granted, i already had a bitcoin testnet node running, so i didn't have to sync the testnet blockchain), i ran into some problems, but cdecker helped me out
In my opinion, the best way to learn about a technology is to get some hands-on experience, and since bitcoin has a pretty stable testnet, you can get this hands-on experience without risking any real BTC (losing tBTC is not really a problem)

Well, very, very, very, very dumbed down and simplified, the lightning network is basically something like this:

Person A opens a payment channel with person B. Person A and B funds the channel using an on-chain transaction of (for example) 10 BTC.
Person A can now send (for example) 20 offchain transactions of ~0.1BTC to person B (for example, person A has a ipTV subscription with person B, and he pays 0.1 BTC/month for his subscription, every month). Everytime, the status of the channel gets adapted with an offchain transaction.
If, in the end, the channel gets closed, the final status gets recorded into a transaction and broadcasted to the network.
So, in this case 18 on-chain transactions were avoided, only the funding and withdrawing transaction were on-chain.

Now, imagine person C. He opens a channel with person A.
He can now send 0.1 BTC to person B, since person A has an open channel with person B, and the channel is still funded. So in reality, person C sends 0.1 BTC offchain to person A, person A sends 0.1 to person B, so person B receives the 0.1 BTC that was sent by person C. Person's C available funds are reduced by 0.1 BTC, person A still has the same amount of funds as before the transaction, person B has 0.1 BTC more than before the transaction (fees were not taken into account with this very simplistic example)

When sufficient people have open (funded) channels with eachother, you can basically send funds over the lightning network to any person that has at least 1 or 2 open channels. Each node in the network can add a tiny fee, but it is also possible to minimise the fee by calculating the optimal path between 2 nodes/wallets/people.

If they have the key or the seed, there is no way to lock the wallet... They can export the seed, xprv or private keys, so they can spend the unspent outputs from another desktop wallet, no matter what you do.
Legally, it *might* be your account, but in reality, it's owned (or at least controlled) by the person that hacked you.

Some things don't add up... If you have a seed phrase, by defenition you're not talking about a watch only wallet... If you have a seed phrase, and know the derivation path, you should be able to restore the wallet itself (you can caculate the xprv, from which all private keys => public keys => addresses can be derived).

A watch only wallet is usually created by just entering the bitcoin address. If the only thing you have is the address, but you have no access to the private key nor the seed phrase, there is nothing you can do to secure your wallet.

Truth be told, there is no real way of "locking" a wallet. Sure, a web wallet provider like blockchain.info can block access to a certain wallet, but if a stranger gets their hands on your private key(s) or seed phrase, he can just import those into bitcoin core or electrum and spend all your unspent outputs, even if blockchain.info blocked access to this specific wallet.

Well, there are lots of things you can do, but rather than re-inventing the wheel, i'll point you towards a thread made by Lauda:
https://bitcointalk.org/index.php?topic=1629118.0

Personally, i think the best way of earning bitcoins is to offer an online service and get payed in BTC. If you don't have any online skills, you can always take an IRL job and convert part of your income to BTC (sounds stupid, but without online skills, you're usually better off with a minimum wage IRL job, you'll probably make more per hour than doing something like claiming from faucets)

A ponzi is a sort of scam, it's when somebody is paying early investors with the money they get from late investors, then run away when their "hot wallet" is containing a lot of money from late investors they haven't yet payed out to new investors.
I have no idear what this app you have there is, a ponzi is probably a bad theory, it's probably some kind of faucet.

That being said: i personally think there are better things you can do with your time than claiming from faucets.
Your app pays 1 sat/minute, that's 1440 sat/day. At current preev rate, that's only 16,5 cents/day to keep your cellphone running 24/7... Doesn't sound like a good deal to me

Even worse, if you want to withdraw your "earnings": https://bitcoinfees.earn.com/ teaches us that at this moment, the ideal fee for a "standard" withdrawing transaction is ~52k satosi's... You'll have to "mine" for a month to "earn" sufficient satoshi's to even pay for the mining fee for withdrawing your "earnings"

If it's paying 1 sat/min, it's defenatly a faucet or maybe even a ponzi disguised as a mining app... OR it might be mining something other than bitcoin and converting whatever they're mining to bitcoin.
To be honest, i try to keep such apps off off my phone, so i can't verify it myself. But the facts are pretty clear, a cellphone CPU (or GPU) can never deliver the hashrate needed to make some real profit, and since it's a CPU/GPU and not an ASIC, the energy consumption will never be on par with the power consumption of an ASIC.

This topic has been discussed numerous times... No, you cannot mine BTC using a cellphone.

Just in case you don't believe me, i've created an auto-updated script that basically proofs how much you'd lose in power bills if you even attempted mining using your cellphone's CPU:
https://www.mocacinno.com/nonspecialisedmininghardware.php
On this page, look at the line calculating the "profits" for mining with a cortex A9 (a cellphone CPU), if you pay 0 cents/Kwu for your power, you'll make a whopping 2 satoshi's per year (mining 24/7). I'm firmly against using faucets, but compared to cellphone mining, faucets are great, they give you a revenue of 50-100 satoshi's for 3 minutes of work, you'd have to mine many years to mine an equal amount with your cellphone.

This script does not take into account you'll probably overheat your cellphone, breaking it, or damaging your battery.

What's stopping me at this moment is that i've been running a c-lightning node on the testnet for allmost 2 weeks now, and at this moment, it looks like the project is still to immature to run on the main net.
I look at their issues, and i see dozens of issues popping up every day. The main dev looks like a great guy, he's really dedicated to his project, and he fixes most issues right away, but still, i wouldn't be confident enough to run a node on the main network right now.