I've found that compiling a simple 'hello.c' with the command line
gcc -s hello.c -o hello.exe
makes AVG think it's a virus.
Adding the -O2 -Wall options doesn't do this.
Anybody else care to try it?

What version of Vista? I've got Home Premium and use MinGW regularly, however I don't have AVG, I use Symantec Endpoint Protection (where I work requires it be installed for VPN access).

I could probably throw AVG on here quickly enough to test though. What version of AVG was it? The free one?

Vista Home Premium SP1
AVG Free Edition Ver. 8.5.375

I don't think Mingw is "making a virus", it's just kind a kind of comical misidentification. Send your enemies a "virus"!

I've had that once with a different antivirus and my own game compiled by MinGW. The "problem" disappeared when I've written more code for the executable .

It's just caused by the antivirus applying broad heuristics to executables, which sometimes results in false positives. Fortunately, changing a few bytes around (which will happen when you write some more code or change the existing lines) will make it register as safe again.

I have never had AVG pop up a warning like that on Vista...

Perhaps it is a virus on your computer that is infecting the executable after it is created. That has happened to me before, but it was on a Win98 machine and another on an XP machine...

Run the EXE through virustotal and see what you get...

I've also seen AVG complain about an innocent .ini file from a windows 95 game...

Actually AVG is complaining about that dll that has libc in it, the actual exe is then able to weigh in at a svelte 5k.
Seems to me that the non-infected version with -O2 would use that same dll.