I just changed Avira Antivirus (in another machine) to Avast. I then noticed that while using Explore Image feature from Acronis True Image (v7.0 build 638) the computer hangs and become completely unresponsive needing a (cold) reboot. There is no problem with image files (verified) so I thought it might be the antivirus exchange. I removed Avast and reinstalled Avira and voilĂ , Acronis became fully functional again. Turning off active shields didn't help at all, most likely because the culprit may be an Avast service.