I wonder if anyone recognises this...

A while back, I went to one of my aunts to re-install her computer, but before I started, I noticed something odd: on the desktop, in the top-left corner, a small, white triangle (filling the corner) was visible. It wasn't clickable - I could not find any functionallity whatsoever. After I checked if it could be the desktop-wallpaper (which it wasn't) I descided formatting would delete it anyways, so I went on and reinstalled the computer completely. Sure enough, it was gone afterwards.

Today, I'm wondering. What could that little triangle have been? Installed on the computer was Win98 (either SE or the original, I don't remember) with a standard green-blue desktop. The triangle wasn't very big, about 5 pixels in width on a 1024x768 desktop. No-one had noticed it before, but there's no telling how long it had been there.

Anyone, any ideas?