My internet is going crazy, websites are popping up on their own... Help?

[Raiden94]

So here's the deal. I've been using Explorer for 3 years now. Please don't start with the whole "Explorer is ancient, go with Firefox or whatever". Thank you.
Anyway. recently this website has been popping up like crazy:

http://pp.developunit.info/z/?eid=35&hi ... 1717025221

Everytime I open a new link, this website interrupts the loading of the page and takes over. When I press the "back" button, nothing happens. When I refresh, nothing happens. Basically I have to keep trying over and over and over until I get lucky and the page loads propperly without interruption. It's annoying as hell.
Sometimes even when a page has perfectly loaded, that website just decides to take over.
I have no idea where the hell it came from. It only started appearing recently, like less than a month ago.
What do I do to get rid of it? And inorder to stop it from happening again, can you tell me what triggers it?