IE closes after five minutes

[iolair]

I have three users on my LAN that have the same problem. We're running XP Pro, with IE 6. All three have been scanned for virus using Symantec AV Corporate Edition, and all three have been scanned for adware and spyware. After five minutes of internet useage, these users experience a disconnect - from the browser. They can still work with network resources, but can not use the Internet again until they reboot. I've searched MS's site, with no luck there. I'm looking at the event logs in XP now, but don't see anything unusual. Is this some type of malware our Symantec won't catch yet?

Iolair MacWalter
Director of IT