Tiny bug running across my monitor!

I've read around the Internet and a couple threads on Discussions about this, but I've not seen any cause/effect/remedy.

Today, I noticed a tiny bug running around on my monitor. At first, I thought it was real, but I quickly figured out it's virtual -- but the cause is unknown. Naturally, I'm concerned about system integrity -- a malware scan is clean, we run Sophos on our systems.

It just keeps appearing and goes away. It's a tiny little dot, so there's no point in trying to post a pixelated image of it.

Does anyone know *** is causing this? From what I've read, this has been going on for some time now, so I would hope someone (Apple?) has figured it out.

Thanks.