I write PHP applications for the company I work for. I spend a lot of time recently working on improving the security of the forms on clients sites to prevent php injection and spam. I'd like to know what other developers out there use to test the security of their apps? Can anyone recommend a checklist, or a site which might check form / application security?

Two friends recently bought laptops independently from Dell, the Inspiron 1300. I was surprised when it arrived, a good looking robust machine with built in Wireless and a very fast delivery. Booting into XP home a lot of software was pre installed, Google Deskbar, several Mcafee products, Dell Support Assistant etc. After a minuter or so running, both laptops experienced the blue screen of death. I uninstalled all the software that wouldn't be used, my friends had bought these laptops for email, IM and word processing. They are both very stable now and run smoothly, I have installed MSN messenger, Firefox and AVG instead of Mcafee. Have other people experienced these problems with Dell laptops? Will they be stable now without so much pre installed?