I just downloaded Agnitum outpost firewall free version 1.0 - and it's brilliant!!!! Also stops ad;s and pop ups as well!
Have tried Zone Alarm and found it annoying and difficult - Outpost is so simple and easy to use so it gets my thumbs up.
AVG anti-virus has to be the best free AVC software I've found too - get it and forget Norton and their high prices - they also stiff you for more money after a time when you need more updates.
Panic Ware pop-up stopper is brilliant for stopping er.... pop - ups so I would also recommend this as it is a must and makes surfing the net a pleasure again.
Hope this helps someone.