Well, you have no VAC ban on your profile so whatever it was, was temporary. You can breathe easy now.

Maybe the admin of that server was messing with you.
Try that server once more and If you get it again take a screenshot.

However, if you play on a different server and you get the same thing then the problem is in your computer. Still take a screenshot.

Perhaps this was a flash movie or image of Blender playing in the message of the day box? Anyway, screenshot it, but hope it doesn't happen again.

Thank you so much... I can breathe easy now. I was scared if I was VAC banned or if I was going to get VAC banned or something. I didn't understood this because I never cheated or hacked once in my Steam history. Anyways, it's not happening anymore.... at least not now. It happened when I was in a combat, so maybe the admin WAS messing with me. By the way, the thing forced me to go to my desktop, and opened the black tab. It was really weird.

I hope this won't affect me..... the last thing I need is to get VAC banned and lose all of my precious Strange Diamond Botkillers.

I don't think it was the admin. I think it was just some window that automatically appeared in my window. I installed a few games on Steam, Steam itself, Facebook, Blender, Wings 3D, and that's about all of the software that I installed. Thanks for the information and advice. What do other people think?