I would like to be writing a positive review since I have been impressed with this program in the past. It has a slick interface and is FAST once it completes it's overall scan. I upgraded to X4 and found that it crashed constantly (upon finding a virus or corrupted file). I tried it using another machine with a freshly installed OS (10.4.4) and a recently formatted drive and got the same results. I have two large drives with actual viruses and it took me over three days to scan them both using this program due to all the crashes and having to start again. I ended up being forced to purchase Norton version 10. It may have an ugly past rep (version 9) and the interface is ugly, not to mention slow, but it found viruses X4 missed and while it may have been slower initially, it never crashed. Perhaps the issues are fixed in the last update X4 just did, but I can not click on the X4 restart button and am going to have to force quit it. Too many crashes for me. I have switched to Norton which seems to be more stable and yes, It was crashing before I installed Norton.