As stated in the FAQ there are no virii in the ads.
You should scan your computer for viruses with
with one of the following
Ad-Aware:http://www.lavasoftusa.com/ (free)
Microsoft AntiSpyware:http://www.microsoft.com/downloads/details.aspx?FamilyID=321cd7a2-6a57-4c57-a8bd-dbf62eda9671&displaylang=en  (free)
Spython: http://spython.com/  (free trial)
(I recomend Microsoft AntiSpyware)
and scan for viruses with any reliable anti virus software.

Explanation:
 Spyware can sometimes download files from anywhere and install other spyware or viruses, therefore the spyware should be removed.
An anti-virus scan should remove any viruses that already may reside on your computer.

I am not an employee of T35, I can tell you unbiastly that there are none for several reasons:
The biggest beeing that the US govournment does actualy take down sites that have viruses (and distributes them) (as much as we like to pretend gouvernments do nothing)
T35 uses respectable ad agencies such as http://www.yesadvertising.com/. If there were viruses, T35 would lose money due to law suits rather than gain any from displaying viruses.
The ad pages are all static/javascript and sometimes flash.
The ads sometimes place a cookie (a small text file) on your computer to let the ad script know you've seen this particular ad before. Some anti/spyware/virus programs tell users that cookies are spyware when infact, they do not harm your computer any way besides taking a small (very small) portion of space on your disc.
Low security browser settings may let viruses/tojans/browser-highjackers to be placed on your computer with out you knowing it.