I recently upgraded to Spyware Doctor 5.0. Randomly when I shut down I get the blue screen with a message that a problem was detected and windows has shut down to prevent damage to the computer, with a dump of physical memory. The problem seems to be iksysflt.sys, which is a file in Spyware Doctor 5.0. (I have version 126.96.36.199, and had no similar problems with version 4.) I googled this file and found several forums that mention this problem, including PC Tools' own forum. Apparently there is no harm being done, and as I said the error does not occur consistently. It's a bit disconcerting though, especially since PC Tools has not fixed this bug.