Why do skull icons appear on some video files? What could that be?

December 31, 2013 at 02:20AM:

I had an old CD from which I copied some files to my PC. While copying, Avast detected a virus named “Win32:Evo-gen [Susp.]“. Okay, but after about half hour I see that MP4 videos on my computer have skull icons on them and when changing the icon’s size the icons change to some danger type cross. I restarted my PC and the icons were gone. Then I ran a full system scan and nothing was found. Should I be afraid of something?

Please see images of those strange things -

Skull icons – http://i.imgur.com/Xz5A7Qk.jpg

Icons after changing size – http://i.imgur.com/Kk2xBG2.jpg

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