It seems that lately there have been a lot of security vulnerabilities found in many of the most commonly used software. Unfortunately, many of us don't have the time (or desire) to go through all our installed software looking for updates just to stay safe online. Here's one solution; instead of having to subscribe to vulnerability reports and sift through security advisories (many which have nothing to do with your installed programs), you can rely on software that let you know when updates are needed.
Secunia Personal Software Inspector is like a Virus Scanner for your software but instead of looking for Viruses, it looks for older versions of software that are known to have security vulnerabilities and advises you if they are found on your computer and if newer, more secure versions are available. If you prefer not to install any new software, there is also an online version available but unlike the Personal version which identifies over 4,700 programs, the online version only identifies 40 of the most common.
As a side note, having up to date software won't make much difference if your Operating System (Windows XP, Vista, etc) is not up to date and secure. Visit Windows Update at least once a month (and Office Updates if you have Microsoft Office installed). If you prefer, you can enable automatic updates and avoid having to check for Windows updates manually.