I vote for the dumb users! Its amazing on how many people call the helpdesk after being infected from a dumb choice. For Example a few weeks ago one user calls me and has her laptop infected. She had opened a email that was supposed to be tracking information from a UPS package. This was strange as they worked in the finance dept, I asked if she was expecting a package and she said no. I looked at this email and the tracking number wasnt even in the UPS format (All tracking numbers, at least in the US, start with 1Z)