NIS messing with my lag

[JTsnow]

When Nortan internet security is enabled, my lag goes through the roof, usualy i have the worst ping on the server. When I disable it i have a normail ping. However when i am not using the source engine ie: DoD, even with nortan i get a normal ping. So whats the problem? CS:S needs a certain port opened or is there something im missing?
btw, although disabling nortan fixes the problem, i do not like the fact i have no protection against attackers. I have already been attacked twice within the last month so i would like to have nortan enabled if possible

 

[Ecthe|ioN]

I've noticed the same thing too. Only in CSS. When I check the ping of a server from the desktop it could be at like 70-80, ingame it boosts to 200, and stays there. The strange thing is that this doesn't happen on all servers.. Just some of them .. *scratch head*

 

[JTsnow]

With mine, when i look for servers not one of them are under 100, but when i disable nis they are normal, like 10-45 on the first page. and its not on just some servers for me, i tried about 5 servers before i figured it was nis.