1. This is a targeted hack. Does that mean that the attacker probably had a way of knowing that cwwang had those kind of funds stored? I have heard of malware that randomly just scans computers to pick up presence of wallet.dat files?
If it was a targeted attack, the attacker must have known about cwwang's crypto holdings, otherwise it wouldn't have been a targeted attack.This being said, there's plenty of malware that's included into many real and fake programs, usually tools that have something to do with crypto, meanth to infect as many people as possible in the hope of finding a wallet, or copy/pasting keys, or copying the thief's address whenever a btc address is placed in the clipboard.
2. How to classify such attacks? What are the ways in which it is possible to lose all your keys from a network connected PC?
Don't know about the classification, but sure, if your wallet is compromised, it's usually all keys that get stolen at once. 3. Is there any Standard Operating Procedure where you can run a wallet like electrum on a network connected PC (for small, normal transactions) that would ensure that malware/ keyloggers don't get access to your computer?
Hardware wallets.There is no other procedure that can give you > 99% protection while spending from an ONLINE pc. There are plenty of really good procedures for airgapped wallets and paper wallets that are at least as safe as hardware wallets tough.
4. Suppose a keylogger is active on my PC. Shouldn't it be possible to see it in background activity as some undefined/ random process (Talking about Windows).
I'm not a windows admin, i don't really like windows OS, but to the best of my knowledge, not all malware can be seen from the taskmanager... Rootkits, taskmanager vulnerability's, replacing the name of system components,... 
