It's common to hear security vendors advise people to "keep their computer up to date with the latest patches" but what does that actually mean and why is it important?

Malware can infiltrate PCs via a number of attack surfaces, one of which being bugs in Windows and the programs on your PC.

One famous malware outbreak, the Conficker worm, was able to spread so far and wide due to a bug, or "vulnerability", that it exploited. The vulnerability, known as MS08-067, allowed a successful attacker to run malicious code on the machine.

Interestingly, this vulnerabilty was patched in October 2008 but the worm itself was discovered a month later in November. Even though a patch was made available to fix the exploited vulnerability, the numbers of infected machines continued to skyrocket, suggesting that computer users were simply not updating Windows. The message is clear - make sure that Windows is set to install updates automatically.

Vulnerabilities affect programs as well as Windows. In the last few weeks some common applications have been updated to patch security problems, such as Google Chrome, iTunes, Adobe Flash, Air and Shockwave and Firefox . Some applications will update by themselves, but it is worthwhile to take some time to make sure you applications are up to date. You can usually find a "Check for update" option if you click on the "Help" menu item.