Non-parody impersonation is a violation of Twitter's terms of service. Let Twitter squelch that account for you.
ADDED: Glenn says:
JUST TO BE CLEAR, I don’t think the Instapundit feed on Twitter is any sort of a scam. I think it was just set up by someone trying to help. I just want to upgrade it and need the keys. I figured it would be easier to ask the person who set it up for me first, rather than going through Twitter.I can see why he'd want to take over the existing feed rather than eliminate it and start over, and while the person who started it may have meant well, I do think Glenn needs to control his brand. I assumed this Twitter feed was his and formed the opinion that it was awfully unimaginative. And as Jason (the commenter) notes, the fake Instapundit was following various Twitterers: "It's like Mr. Reynolds is endorsing them and I wonder if payments are being made for the follows." Well, that would be a scam.