It's all but impossible to keep track of updates to all the software on a Windows computer, but Secunia offers a free service that's a great help.
A new report shows that Apple has the most software vulnerabilities of all major software vendors, though it doesn't address severity or how fast holes get patched.
The excellent Online Software Inspector has a couple new minor problems. Still, it's a great service for anyone running Windows.
A nontraditional test using exploits instead of malware shows that traditional security suites fail.
Photoshop CS3 (#6): Two major security vulnerabilities extant, according to Secunia; continued installation issues
Secunia: Virex for Mac OS X security flaw reported, patched
Secunia: "shared_region_map_file_np()" Denial of Service in Mac OS X
Secunia: Mac OS X ftpd Buffer Overflow Vulnerability
Secunia issues Safari vulnerability advisory
Secunia issues "less critical" OS X security alert