Took me a while to realize that what I'd originally thought was a smudge on the screen was an image on the background.
First I thought, "oh carp, got a smudge" -- so I cleaned the screen.
... but the "smudge" didn't go away! "Oh *&^@%$ I damaged the screen!", I thought.
Shrugged, then thought "Oh well.. gonna have to locate a replacement eventually," so I opened a new browser window to start shopping for a replacement.
"Eh?!?" The "smudge" is gone! Went back to browser window with Universal Thread and the smudge came back.... Wait... there's something really odd going on... Around that time I'd hit the maximize button on the browser window and finally noticed in a blank area that there was an image of a globe on a gradient background... Ah! that explains the "smudge" (didn't recognize the globe image because most of the time it was covered over by text)