There is certainly no shortage of products and services on the market that can help you protect your network from attack. But here’s one that’s free (provided you’re running Vista): Address Space Layout Randomization (ASLR), which moves around function entry points in your system’s memory to make them harder to exploit. While ASLR might not be able to prevent a targeted attack, it can help defend against automated attacks. The only caveat is that for ASLR to function correctly, your machine must have Data Execution Prevention/No eXecute (DEP/NX) enabled within its BIOS. To find out how to determine whether your PC has DEP enabled or not (most machines will have it turned off by default), check out the full article.

For more information:
– see this Ars Technica article