[Horace]

Change your WPA password. If you're using the standard supplied Sky router with default settings then the password can be calculated using your mac address. If someone else is using your wireless connection then no AV in the world is going to help. Regularly changing your WPA password is good practice anyway, no matter what kind of router you're using.

As for the comments regarding firewalls and botnets. Firewalls are basically useless since most malware uses reverse connection these days. Zone Alarm *may* give a warning tho' I wouldn't rely on any software based firewall especially one as common as ZA for obvious reasons. Best practice is to keep an eye on logs and monitor all outward wan connections for unusual activity.