So a long time ago, like 1998 long ago, we were running on these Windows NT 4.0 workstations that were joined to the local windows domain. Terrifically crude stuff by today's standards, sure, but it is what we had and we liked it.
One of the things you could do back then (as today) was to set a pre-password dialog box on the computer. Presumably this was for the critically useful "thou shalt not log in to this computer if thou be unauthorizedeth" messages. But this dialog is customizable. So on my co-worker's computer, I set the pre-login prompt to have a title of "ubx32.dll" and a message of "Success!" It looked just like a pseudo-error box that every other application would pop up, and "ubx32.dll" seemed like a plausibly anonymous name of a NT application dll.
So every time he pressed Ctrl-Alt-Del to log in, his computer would show him this dialog, complete with an OK button, which he'd have to clear before he could log in.
And then I forgot about it.
A year later, I happened to be at his desk, and he has a little yellow sticky on his monitor, with "ubx32.dll??" written on it. And I laughed, because I suddenly remembered about the prank. And of course I had to let him off the hook at that point.
He said that over the year it had been appearing he'd probably wasted about half a day on googling around trying to figure out what the hell was happening to his computer.
