Games minimize randomly/roughly hour long intervals

[MrEasy]

Hello there,

I'm at the end of my rope, so I hope you guys can help.  My wife's system just... cuts to desktop.  It's not a crash--she can click on the minimized icon to immediately pop back into a game, but it certainly makes things difficult when we're playing--well, just about anything.  (It's added an interesting dimension to Hardcore Diablo 3.) It happens on Steam games and non-Steam games. I'm not certain if it happens on any other full screen applications.

I've looked for obvious programs running updates or update checks without success.
I've looked at the usual suspects: security software (firewall, antivirus, anti-malware), no effect. 
I've tried checking the Event Viewer and Task Scheduler to see if there was something running in the background at those intervals.  I saw that Adobe Flash Player had something scheduled roughly like that, so I disabled it.  No joy.
I jumped into regedit and adjusted the Foreground Time Lockout value, no luck.
All her drivers are up to date.

I'm stumped.  I still suspect it's another process that's screwing things up; I thought about trying to figure out how to log start/end times for processes, but most methods I saw involved some kind of polling, like every 2s or so which won't catch the culprit if it's too quick.

Anyway, her specs:

OS: Win 7 Home x64 with Service Pack 1 (Legit)
Processor:  Intel i5-3570 3.4 Ghz
Gfx: EVGA Nvidia GeForce GTX 660
Mobo:  MSI Z77A-G43

I'll take any help I can get.

[DaveLembke]

Just wanted to throw this out there.... once a user complained of same issue and it was because they were accidentally bumping the Windows Key. The fix was to pry the key up and remove it so that it cant get bumped while frantic fingers are at work when gaming. If you can carefully remove the windows key and see if that solves this, it could be the cause. 

The user was using WASD directional controls and accidentally bumping it between the left CTRL and ALT key. They left the right windows key intact, but you can pop that off safely too maybe.

[MrEasy]

Hehe.  I wish it was that simple.  I can say with absolute certainty that it isn't an accidental bump on the windows key causing the issue.  While trying the different approaches I described above I'd make a single change, then boot up Goat Simulator 2014 and leave it on while I was working on the adjacent computer--pausing only to move the mouse around every now and then (to prevent any possible idle response causing a similar effect).  Every time, the game would minimize after about an hour or so. 

[BC_Programmer]

I've seen this occur a few times. In each instance, it was caused by malware.

[DaveLembke]

Based on this statement, I didnt suggest what BC suggested, but BC is right if you have one that is well hidden.

I've looked at the usual suspects: security software (firewall, antivirus, anti-malware), no effect.

What software have you used for prevention and detection?