If you become a fan of McAfee on Facebook, you are able to receive a free 6 month subscription to their Internet Security software package, worth £24.99.
Be warned, they require payment details for future automatic subscription renewals, but they don't take any payments from you for this 6 month subscription, and you can cancel the automatic renewal before your free subscription ends.
I've used McAfee for years, and it has always done me well! Enjoy!
Edit: I can't seem to get the direct link to work, the Facebook page is here:http://www.facebook.com/McAfee
And once you've become a fan, check out the "Protect your PC" tab