Spend £30 at amazon.co.uk on products sold by them (not marketplace) to get Kaspersky Internet Security 2009 half price.
Follow the attached link for full details.
To get this price you will need to enter code NETSCRTY at the checkout.
This is by far the cheapest place to purchase this from. Amazon is already the cheapest before the 50% discoung!
Don't forget to go through Nectar to get the equivalent of 2% cashback.