I am running Windows Vista and an icon has appeared near the clock at the bottom right of the screen. You cannot click on it (right or left) and it. When you look at it in the Custom Notifications Icons screen, it shows where a name normally is. It is not on all the times, just periodically.

I've attached a screen grab of it and I've marked it with a red error to point out the icon in question.

I run a full antivirus program that scans every night, so I know it's not a virus.

Any ideas?