You must keep everything patched and up-to-date on your computer. While you obviously need to keep your operating system updated, you should keep your applications and plug-ins updated as well. Several tools that can help to keep track of any available updates are listed below.
Check Your Plug-ins for Updates
Qualys BrowserCheck is a free service that checks if your browser plug-ins are up-to-date. If a plug-in has not been updated, you may update it by clicking on the Fix It button next to the name of the plug-in. The check should work in most major browsers.
Be sure to run it on all of your browsers, e.g. Chrome, Firefox, Internet Explorer (Windows only), and Safari.
Check Your Applications for Updates
Windows: Secunia OSI is an online scanner that checks your applications and plug-ins for any updates. It does not take very long to run and will provide links to the location of the updates should any be necessary.
Mac OS X: You can check for basic software updates by going to the Apple button in the top left-hand corner of your screen. In the pull-down menu, click on Software Updates... This will allow you to install any Apple-related updates.
AppFresh is a service that allows you to check for both Apple and non-Apple application and plug-in updates. However, this is a very new program and may have slight bugs that still need to be resolved.