One of the most common ways to get a virus or malware infection is to have out-of-date browser plug-ins. We’ve all seen those annoying pop-ups asking you to update your Java, Flash, Shockwave, or Adobe Reader, and it’s awfully tempting to just click “ignore.” But doing so is equivalent to neglecting to change your locks after your keys have been stolen.
Typically, when these browser plug-ins receive updates, it’s to patch a security vulnerability that’s been discovered — often, one that will allow a hacker or malicious program to take full control over your computer.
Not sure if you’re up to date? That’s okay — Mozilla has done the hard work for you. This site, which will work in any browser, will tell you which plug-ins need updating, and supply you with a handy link to download said update.
Source: Mozilla Security Blog