Your node would have to rebuild the chainstate by going through all the blocks that you've already downloaded and synchronized. I'm not sure if deleting it would actually require the blocks to be validated again (achow101 said Core does). Anyhow, you can execute -reindex-chainstate to rebuild the chainstate only and that wouldn't need to validate the blocks again since your client is getting the information from your already compiled block index.

If you have a spare hard drive, you can think about synchronized it first and copying the entire data directory to it. If it gets corrupted again, you can just replace the data directory.

If its confirmed, no one can help you. Bitcoin transactions aren't reversible.

If its an inside job, then you would have to prove it which is fairly unlikely. The IP wouldn't help much either, they can't prove anything and the attacker would've probably used a proxy of some sort to mask their identity. You should be looking at the ways that you got hacked; do you have a malware on your computers/phone or was your password used across several platforms etc.

It really depends a whole lot on your type of usage. If you're running it primarily for your own use, you probably don't have to maintain too many connections and use too much bandwidth.

If your main objective is to help Bitcoin, then the more connections you have the better it would be, possibly requiring you to use more bandwidth. The main factor affecting your bandwidth usage is possibly your kind of peers.

Anyhow, limiting your connections should be enough to mitigate the problem of running out of bandwidth.

No. The transaction will appear in the mempool till the individual nodes decides to remove it or if it gets mined. The transaction does not simply disappear; its either you "get" your coins back or it gets confirmed.

In the event that the unconfirmed transaction stays in the mempool of a node for too long, the node can decide to remove the transaction from its mempool. If you're using Bitcoin Core, your transaction should disappear the same time as the other nodes. When this happens, it would be as if the UTXO has never been spent. If you don't want your transaction to be dropped, simply rebroadcast it (some clients do this automatically).

Electrum does not convert your current wallet into addresses with bech32. Install the latest version of Electrum, go to File>New>Standard Wallet>Create a new seed> Segwit.

Take note that you have to backup both of the seeds since they are not the same at all.

It's okay. The seed option is just for HD wallets which can be used to restore from a set of seeds. They are generally easier to use and backup. Without that, you have to ensure that you keep your private keys safe or keep several backups of your wallet.
You can import the wallet file into your Electrum and you're good to go. You would be prompted to create a new wallet and you can restore it by going to File>Open after creating a new wallet.
I would really recommend you to keep a backup of your wallet.dat file regardless. You can delete everything in your data directory without issues, if you have backed up your wallet.dat.

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I can't think of why you aren't choosing to just send everything to a new address covered by the seed. Your privacy is lesser with the imported keys since change address aren't used.

No. If I understand correctly, he meant that it is optimal for the miners to be in direct connection with each other and hence are able to get the new blocks the fastest. When a block is mined, the propagation of the block throughout the network can take quite sometime; potentially up to several seconds depending on your connection. If the propagation is this slow, the miner is losing on time to potentially mine on the next block.

The government can certainly block the direct linkage but the miners would still be able to get the block data by connecting to other peers. It's also hard for the government to fully block any connections.

Just to be sure, you restarted Core when you've changed the wallet.dat right?

Are you sure that you've replaced the file with the correct wallet.dat? Bitcoin Core should automatically rescan the wallet file when you've replaced and restarted the client. Did you mix both of them up by any chance?

Wooopsss. Looks like someone is illiterate!

Nothing.

Signing message uses a signature and an address to validate. When the message is signed, a private key is used and the public key can be derived from its signature. With P2SH addresses, there isn't a public key for the client to use and it's just a script. You can't sign with P2SH/P2SH-P2WPKH as of now.

The standard for sending transactions at the beginning was actually directly to the ECDSA public key (P2PK). It was changed only after awhile to public key hash. The main advantage to using SHA256 as a method to send address is that it is way smaller than public keys and hence more convenient to store and type. The added advantage is that there isn't any known attack against SHA256 as of now but ECDSA is susceptible to quantum computer attacks due to Shor's algorithm.

Since your public key isn't exposed till you spend your coins, your address would likely be safe against it.
One obvious disadvantage is that it would require a hard fork to implement it in Bitcoin. I can't think of any significant advantage for Keccak over SHA256 since there isn't any glaring vulnerability about it right now.

No, its because you don't have a valid collateral.

If the first user spends everything in the wallet file.
No. If the first user doesn't spend the coins, the coins are still in the addresses that is also in the same file that others can hold. The user needs to spend the coins, even to his own address in the wallet with new password.

Logically speaking, no one would ever successfully crack the wallet file and not spend the coins to an address they control exclusively immediately. As said, I'm not sure why you're asking this but don't ever buy an encrypted wallet file from anyone.

Bitcoin is not anonymous. Transactions are supposed to have an input and an output with it. Without the public key in the transaction, the signature cannot be verified and hence the transactions cannot hide their origin addresses.

As per most wallet behaviors as of now, they discourage address reuse. Each of the addresses are supposed to be used only once and hence all the change are sent to a new address and a new address is given in your wallet when the previous gets used. With this, no one can know whether the address in the other output is yours or if the coins are sent to another person.

Private keys can be used to derive the public key and its hash which can in turn allow the wallet to identify all the relevant transactions related to the wallet. The main function of the private key is to sign the transaction.
Incorrect. Private keys are the main thing when making a transaction. Without a private key, the transaction wouldn't have a signature and it would be invalid. Private keys are used to generate a signature to validate that the inputs can be spent.

Everyone that runs a node will validate the signature, not only the miners. The miners have to check the validity of the transaction first before generating the merkle root and try to mine a block.

No. Assuming that the addresses all have one UTXO only, this would be the scenario:
Bitcoin Core doesn't reuse addresses. If user A encrypts the wallet, any future addresses will be different. If User A spends the sole input for the address, the change will be spent to a new address that User B will not control.  Since the addresses generated by User A will be different, User B will not be able to spend anymore Bitcoins.

If you have multiple UTXO in a single address, Bitcoin Core will automatically choose inputs that is suitable for the transaction and in some cases, not all of the UTXO will be spent. Hence, the other user will be able to use the remaining UTXO that is not used in the transaction.

That's normal.
It is not a hack and it is generally the common behavior over the major wallets. When you spend an unspent output in your address, you're spending the output completely. This means that any value that is in that output has to be spent or else it is recognised as a mining fee. As such, the wallet automatically creates an output in the transaction to spend the remaining funds not used as mining fee into a change address[1]. The change address is hidden in Bitcoin Core by default but you can choose not to use it, at the expense of privacy.
That's correct.

[1] https://en.bitcoin.it/wiki/Change

All denied sorry.

Isn't it the opposite? In a decentralised system, the lesser users there is, the lesser hops is needed for the information to be passed around and the faster it would be.
It doesn't exactly ensure security, if I'm reading you right. Whomever having the most number of phones would be able to choose whichever transaction to include.

It is also impossible for app developers to add such mining malwares into their apps without significant backlash.
So whomever that has the fastest internet connection is the winner? How do you know who is the fastest if you don't rely on a central server?

The client doesn't update itself. Nodes running the older client would still be retrieving information using the IPs as in the source code. If they are still working fine, there isn't any issues with it.

It wouldn't cause a hardfork since the clients are still running with the same protocol rules.