Always verify the app upon downloading it through PGP as suggested above, so the best thing that you can do now is to create another one that is safe, or better to buy a hardware wallet for less worry.
I would suggest reformatting the computer first because we have no idea what OP did to have his coins stolen. There could be malware and keyloggers on his system and a fresh Electrum install on such a system is not safe at all.
@OP
It's impossible to single out the exact reason without knowing everything about your online activities and the status of the device you had Electrum installed on.
Are you 100% sure the software was downloaded from the official website and not some lookalike?
How was your recovery phrase backed up?
That address you mentioned has already received over 55 BTC. The person knows what he/she is doing. I see that you already reported the theft on
BitcoinAbuse. Still, I would be careful trusting any recommendations that promise recovery. I am talking about the suggestion someone gave you about using a cyber security agency to get your coins back. That's another scam most probably where they will ask you to pay for recovery and possibly lose even more or get your device infected. Bitcoin transactions are irreversible, and without law enforcement it's almost impossible to find the culprits.
Answer the questions people asked you to figure out what could have led to the theft, so you know what to do and what not to do in the future.
