Ad-Aware and Spybot are free. if you know the right places you can download Norton with a CD Key for free.

Which OS are you running? I'm guessing XP right?

http://forum.theispguide.com/isp-ftopic135.html This looks like it may contain the solution to your problem. A couple of posts talk about finding a value in the registery and setting a port to "0". Other posts talk about downloading a FireWall and installing a patch. If for some reason you don't have a firewall then get ZoneAlarm.

That might be it!! lsass.exe is probably connecting to the net to stop your comp connecting. Get ZoneAlarm (download the free version) and when an alert pops up saying lsass.exe is trying to connect up, tick the "Remember this setting" box and click Deny.

Look through the posts in the thread I linked to as well.

Hope it helps sort our your problem.