Yeah, they just switched over to a pay model. I've been using it for free for almost a year. Most of the IE ad blockers that were free & good have either switched to a pay model or have been discontinued.
IE9 has Tracking Protection lists which acts like a lightweight ad block if you subscribe to all of those (except don't sub to TrustE since all they do is list ones that should be allowed).
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http://simple-adblock.com/
Ah that one worried me as malware.
edit - And they want you to pay for it. Screw that.
If for some bizarre reason you want the IE engine you could just use the ietab addon.
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I've got a spare copy of Portal, if anyone wants it message me.
If they had a few choice ones I might give it a go but as it is now it's not even worth opening outside of taking a quick peek.
I KISS YOU!