If you have Java installed on your computer (and you probably do), chances are you have old versions laying about the place and some of these will be a security risk. But there is and easy way to remove them.
First Go to Control Panel > Add/Remove Programs and remove any Java versions with a number lower than 1.4.2. Really, just uninstall them.
Now visit http://java.com/en/download/uninstallapplet.jsp and let it do it’s work. This tool scans for older versions of Java and removes them without breaking your current version as well as checking you are up to date. Worth visiting once in a while. Or if you have better things to do, just go there now, run it once and chances are you’ll end up being that little bit safer online.