Help! Invisible virus I cant remove/prevent!

OK, so I live in Student Accomodation and am on a network which allows me to access the Net.

for a few weeks now, i've been getting regular popups off Norton alerting me that it has found and removed an infected file. The name of the virus is:

W23.HLLW.Oror.B@mm


When I went home for a weekend, I took my PC and didnt get any of these popups, yet as soon as I went back to Uni I started getting them again.
So it would seem that this Virus is getting to my computer through the Network, yet I dont know anyone else who is on this network that gets these popups.

My HijackThis log is clean, Spybot finds nothing, Northon finds nothing when I do a system scan, yet I keep getting these popups. I've googled and found manual removal instructions that tell me to remove certain files and registry entries, but none of them are on my system, so I am totally confused :s

Help!

Thanks!