The hackers often obfuscate their malware and that's the reason why most anti-virus software and scanners can't find the malware in a system. Of course after reading your posts and reading most of the posts in this thread, I also came to the conclusion that your computer was infected with a malware and that's the reason why your wallet was drained.

I also suggest you to always keep your wallet and wallet related information in a separate system because these days hackers try their best to steal Bitcoin. I would also suggest you to try storing your Bitcoin in cold wallet as that's much safer than the hot wallets. Personally, I also use Electrum wallet on Windows and so far I haven't faced any issue. I must say that I have separate system where I connect my wallet and kept it there and it has been safe for me. However, my holdings are still in a wallet that not connected to internet.