Flash and Adobe Reader: Adobe, like Apple, pushes out security updates as they are completed and issued. Alternatively you can request a update check by clicking Help, and then Check for Updates. In general, you can expect legitimate requests from Adobe to install new updates to appear shortly after you boot into Windows; you should take the opportunity then to install them.

Java: Sun recently ran afoul of security researchers who discovered that insecure older versions of Java remained on the Windows machine the researchers installed newer, more secure versions of Java. With JRE6 Update 10, Sun now removes older versions of Java, but it doesn't remove any pre-Update 10 versions; you'll have to uninstall these yourself. (Note: Not all PC users have Java installed on their desktop; don't feel bad if your system is Java-less.)

Robert Vamosi is a freelance computer security writer specializing in coverage of criminal hackers and malware threats.