@op, I'd suggest a full virus scan on your computer before putting the new software on in case it's a virus. There's free software like malware bytes and free trials of other services like McAfee.
I even advise to burn a bootable CD and scan from it.
Kaspersky or
Avira are 2 pretty good options.
The idea is at the chance the Electrum vulnerability was used is smaller than the chance you have some surprise on your system. Afaik for the vulnerability to be exploited Electrum should have been kept running.
(And yes, I've read that you have Avast on, but no antivirus is perfect).
A single av software on its own is good, but it can be hijacked by the virus in some circumstances, no doubt the theif has tried that to get more money. It also needs for you to be sending a transaction while simultaneously on a website for that call to work if the wallet is password protected. (I'd suggest using preview before the send part and sign and broadcast it so you can verify that anything is acting normally).