Annoying, mysterious popup during startup

It doesn't really need to be said that I'm loving Windows 8 right now. I'm using a developer RTM on a desktop, and before that I have used almost every trial version of it since the Consumer Preview. Perhaps I should get around buying an actual retail copy of Windows 8, but anyway.

I haven't had any major problems with it so far. However, quite recently, I've been having this annoying popup that shows up on the Desktop every time I start this baby up. It's not an ad popup or anything shady like that. It's just an EXPLORER.EXE "warning" popup that doesn't really say anything.

Here's a screenshot of the popup in question.

I am able to close this popup by clicking OK or the X button, and it doesn't really do anything else after that, but it really becomes quite annoying every time I boot this up. I don't remember doing anything that would trigger this popup. I've already installed the latest first-Tuesday-of-the-month update in the hopes that it would solve the problem, but it hasn't.

Does anyone perhaps have a solution to this? Or at least know where I can isolate the problem so that I might be able to solve this myself? Thanks in advance, guys!

UPDATE: u/taw94 over at r/techsupport showed me MS Autoruns, and so I was able to isolate and solve the problem. Thanks for all your help, guys! You were all great!