Ok, so I'm nw here and fairly new to macs. I've got a MacBook pro from the latter part of 2011 and had been running snow leopard quite happily but because I wanted to use iCloud I updated to lion. I had been running the kaspersky 2011 lab on snow leopard and all was well. After the update to lion the kaspersky stopped working. The icon was there but it wouldn't open. I checked their website and they said it was compatible with lion so I tried to reinstall it after uninstalling it. I now know that was a mistake and I should have quit when I was ahead after the uninstall. It wouldn't reinstall and it just crashed the computer - completely. No force quit allowed. Had to power it off and after that the disk wouldn't come out (eventually fixed that by restarting while doing the equivalent of a right click on the track pad). After that it simply would not restart. Went into disk utilities and did a first aid repair on the hard drive which identified a problem with the kaspersky which it had said it had fixed. It still won't restart. I tried to do a first aid repair on my Mac os x system but it won't let me do that. I am now reinstalling lion. I do have another external hard drive that I have used for back up with time machine but its not as up to date as I would like. Has this happened to anyone else with kaspersky? Is it even worth using antivirus with lion? What do I do if reinstalling lion doesn't work?