Subject says it. Not long ago I had to reinstall 4.08m because the .exe disappeared. Now I installed 4.09, and it disappeared again.

Let me guess, you're running McAfee anti virus? McAfee has decided to identify il2fb.exe as a virus for no reason whatsoever, your antivirus is deleting it.

Interesting. You're spot on. The only weird thing is that it doesn't delete the .exe I have in my modded Il-2 folder, and it never did this before until about 2-3 weeks ago.

Anti virus works by looking for "signature code" in each file it examines. The mod .exe is different in places to the un-modded and likely one of those places is the bit that McAfee thinks looks like a virus in the un-modded version.

I've looked for ways to configure McAfee anti-virus to recognize the Il-2 .exe as a trusted program, without luck. It's easy to configure the firewall, but anti-virus not so much. I think it's time to look into a different anti-virus program.

Edit:
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For now I can move the .exe back to the folder when I go to quarantined files in mcafee (which thinks Il-2 is a trojan).