My understanding is that BD free uses the same engine as paid. The only differences relating to Sonar or whatever they call the new tech relates to speed of scans and resource impact, not the detection. If I am wrong then I would like to see a reference please."the difference is that BD detection rate is superb, unlike the plummeting Avast"
I've been reading the recent AV tests. Avast! is not at the very top tier. But its free edition still performs very respectably alongside the paid AVs in the tests. It does seem, however, that Qihoo is passing it and becoming the best performing free AV.
I would like to see Bitdefender free tested, but you know Bitdefender would be horrified by that.