Kura:
Some thing to take in to account as well is that some AVs are known to flag Tor as a virus, I would say that maybe it's a possibility that traffic gets flagged as such too? I've never used an antivirus, let alone one that does traffic inspection so obviously this is conjecture on my part.
Are you referring to tor client operation as well as bridge operation? I run my tor client on a box that I use as needed, and the bridge on a separate 24/7 box.
As an example, when I helped a friend set-up Tor Browser on his Windows machine, AVG reported that tor.exe was a possible virus and removed it, this also happened when we tested the Tor Vidalia bundle. This was simply a filesystem check though, rather than packet/traffic inspection. It was also very recent, within the last week.
Even on the as-needed box I run the client under tor. I've never gotten these alerts when running the client. - eliaz