Spyware, viruses, & security forum: Has someone gained remote access to my Computer?

Hi, I am new to these forums and have a question regarding the security of my computer.

I am using Windows xp sp3.

To search the internet I use a mozilla firefox icon on my desktop.Recently I have noticed it has been renaming itself.I am certain of this as it has changed from 3 of 4 different names in the last month or so.

The latest name is "bb".I googled this and the top search was for Big Brother which also seems very odd.

I have no idea what can be the cause for this but I will explain what I have done to try and combat it.I ran a program called hitman pro which found no threats.I have also done a complete scan with avast which also found nothing.

One thing I though I should mention is that a couple of months ago I used a port forwarding program to open my ports for hosting a game server.I have been in contact with my isp to make sure I have a dynamic IP which I already did.

Im not sure which of the above information is relevant to my problem but it does seem like maybe someone has a limited amount of remote access to my computer, although this renaming of my search engine icon is the only evidence I have.

Any help with this is much appreciated.

Many thanks

Tim