Hi Mosu,
It seems that starting yesterday Avira AV started to see the mmg.exe located in the mkvtoolnix program folder as a trojan (TR/Dldr.Agent.dsqn' [trojan])
Looking on google, it seems kaspersky went for it too:
http://forum.kaspersky.com/index.php?showtopic=172738
That was with v3.4.0 that i had been using since its release.
Gonna install v4.0.0 and report if it happens again.