Honestly, not everyone wants to use cryptocurrency. There is no point of putting a wallet into an OS which normal users use. They won't be interested in opening it and would probably be treated as a bloatware.

Putting programs that isn't necessary just opens up possible attack vectors and complicate things.

If you're talking about these addresses, its totally possible. Addresses are not meant to be generated using methods which has low entropy. There are still some people who generate these addresses, mostly as a joke. The possibility of finding one of these that is being used as an address to transact is fairly low.

You would be better off testing brainwallet out. The possibility of finding coins there is way higher.

The total number of addresses that can be generated is 2^160. There are 2^256 possible private keys. The total number of private keys that could potentially correspond to an address is 2^96.

Neither seeds nor addresses are sequential. If seeds or addresses are sequential, we would have cracked every single addresses used by now.

The human imagination. However, practically the universe would be. If we reach the time where we can bruteforce addresses, we don't really need any imagination (or much) effort to expand the keyspace.

While the addresses technically has the SHA256 hashing during the generation, the speed isn't measured by the hash but rather by the number of keys it generates.

Zero. By the logic of birthday paradox, the least number of addresses you have to generate is 3.65x10^47 out of 1.46x10^48. Even if you can generate 7.92x10^28 of the keys, you are unlikely to find any keys that has actually been used before. No matter how powerful your computer(s) is, you are unlikely to even generate 1% of the total keys that can be generated (2^256).

Assuming that the keys were generated with sufficient randomness.

Nope.

Pre-validated blockchains aren't particularly safe since it opens you up to attacks if an attacker tricks you to be on a fork of theirs.

You can copy the blocks to your data directory but I wouldn't recommend copying the block index nor the chainstate if you are paranoid. If you have a fast computer, rebuilding it wouldn't take a long time.

If you have an okay internet speed and enough ram, consider increasing your dbcache and you should experience a considerable improvement.

A transaction is a lot more complex than that, I just stated the main components of a transaction.

Let me rephrase that for you. For a transaction, it consist of a reference to UTXO + your public key and a signature that can be validated against your public key. I'm confused over what you meant by the previous owner. The transaction is signed by whoever that is control of the UTXO.

The UTXO consist of the information needed to redeem it. You're right in a sense that the creator of the transaction cannot know the public key as the address is just the hash of it. Most of the people currently uses P2PKH in their transaction and the UTXO contains the information about the hash. Nodes can easily get the address using the public key. If the signature matches the public key and the public key matches the address, the transaction will be valid.

Your coin was probably not stolen. If you're using 2FA in Electrum, extra charges could be incurred. Electrum relies on a third party TrustedCoin for them to provide the 2FA for them. Costs are incurred for every transaction to cover their server costs. See: https://api.trustedcoin.com/#/electrum-help.

As long as you're getting the codes from them, your transactions would cost extra to make. If you want to remove the fee completely, you can restore from seed. IMO, the 2FA isn't worth it, considering that it is paid.

First of all, the Bitcoin hacks that you've seen in the news and around the forum has absolutely nothing to do with the protocol itself. So the strength of your SHA256 has nothing to do with them.

Second of all, yes SHA256 is indeed very strong. The main areas for which it is used is in the final step of the transaction (for which we can do without), addresses (we also don't need it), assembling of transactions for merkle root (everyone can do this; they have the transaction list) and the block header. Being able to bruteforce anything faster would only give you a larger hashrate and really no advantage over the other blackhat hacker.

Blockchain.info has been notorious for providing inaccurate information. You have to get your information from other sources.

The network hashrate can't be calculated accurately. The calculation is mainly done by referencing the block interval and also the difficulty. As a result, if varience is such that the network isn't producing block so frequently, the network hashrate would appear to be lower.

The 12.5BTC isn't unspendable, its lost forever. The block reward doesn't have to be claimed. The reason why its lost isn't just because the address isn't a valid address, the value of the output is zero.

Address of the Electrum server if you're talking about blockchain.info.

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Electrum works differently from a lot of other SPV clients. With Electrum, users are required to connect to Electrum servers. The way blockchain.info track the IP transactions is to see who relayed the transaction to them first. If you're using Electrum, the only possible IP address you would see there is the server's. This does not mean that your privacy is preserved; Electrum servers can see all the addresses in your wallet.

A transaction contains the inputs, together with its public key, a signature and the requirements to spend its output.

The wallet address are the public key hash, public keys are a lot longer than that.

Double spending cannot be prevented, no one said it could be. The network functions on the fact that anyone with a longer proof of work is the correct person. As a result, block reorgs could essentially 'remove' a transaction from the blockchain while adding another transaction with the same inputs but spent elsewhere. Double spending would get harder and harder with the number of confirmations. Number of confirmations would not be affected if the attacker owns 51% of the network's hashrate.

That's correct. The protocol rules stipulates that the coinbase transaction must always be present in the block.

In some earlier blocks, the miner had used a bad mining software which didn't claim the full amount. Reference nodes do not enforce a minimum sum of Bitcoins to be paid out, only the maximum. See: https://www.blocktrail.com/BTC/block/0000000000000000004b27f9ee7ba33d6f048f684aaeb0eea4befd80f1701126.

Break the internet. Bitcoin is decentralised and the network is basically its community of users. Any other forms of attacks would most likely be ineffective at shutting the network down completely. Unless you disrupt the primary way for Bitcoin nodes to communicate, you can't kill Bitcoin.

You could consider the scenario of a 51% attack. That isn't as valid since it won't kill Bitcoin, merely discourage people from using it.

Cryptocurrency is created to be decentralised. Does that mean that everything associated with it has to be?

It's simply too hard for an exchange to work decentralised, mainly due to the problem with the AML/KYC policies of the country. Exchange works as an intermediary between the users. While you can remove the barrier by trading OTC, there has to be someone moderating the transactions and make sure that any disputes can be resolved.

Yes. The copy of your wallet.dat will always have the same private key as the other wallet.dat. Your wallet files would never get invalidated, strictly speaking. If you don't touch it, your Bitcoins will not be moved.

Buying Bitcoins would be the far better choice. With mining, you would need at least some space and electricity. Mining Bitcoins would probably not be worth it unless you have quite sometime on your hand and isn't really interested in getting the coins immediately. The most important point to note is that the ASICs can take up to weeks or months to ship and the ROI for your ASIC would grow exponentially. The only reason why some people are mining is due to their relatively cheap electrical cost.

They are routed to your peers. With Bitcoin, there are loads of nodes that form the backbone of the network. They are basically the fundemental aspect of Bitcoin and without them Bitcoin wouldn't exist.

Once you send the transaction to your peers/nodes, they will verify the validity of your transaction and relay your transaction across the network. Same goes for miners who has mined a block. Every node is technically an 'entry-point' where you can send information to them for it to be broadcasted onto the network.

IP isn't the easiest way to find someone. Getting the information about the user often requires a court order from whichever jurisdiction the IP is located in and I'm not sure if they would consider it if its just a relatively small case. The easiest way out is to just say that you weren't the one that did it and they can't pursue it anymore. IP addresses aren't concrete evidence that someone is guilty.
No and no. They can't do anything and you can't track the funds if they've used a mixer.
No. You can offer all the Bitcoins you have in the world. No one can reverse Bitcoin transactions and your Bitcoins are lost.