Dennis got hacked in a similar way to Mat Honan. The hacker stole his Twitter handle and Twitter won't give it back. He could fill out a ticket that someone is impersonating him on Twitter, but the sad fact is he may not ever get a response. It would be great if Twitter had additional levels of security, but they aren't there yet. Twitter isn't making any money and it's a free service, so they're not motivated to really go the extra mile. Twitter has really gotten worse the last few months and anyone who's built their business around it may be making a serious mistake. Same goes for Facebook as well.
He'd be better off using his own website as his central hub and use social media as an additional tool. But stuff like this can seriously damage him.