It made perfect sense. The alias was useful enough. Jim from IT had been useful enough for him. It had definitely gotten to Sherlock, he'd been right there. So close and the man hadn't been able to do a dammed thing. Fool that he was. "I agree as it happens. Name like yours, if people knew who you were then yes, they'd use it. They'd fight back wouldn't they and there's no point. Not here. But I'm getting the idea you know quite a bit about the people here."
Jim hated heroes. Heroes were idiots with dreams beyond their station, they weren't clever enough to be heroes. Only Sherlock was that clever. He was the only one that really deserved the title. But really, turning people into copies of himself and being happy with this woman being on his side. Jim would be disappointed if it turned out there were feelings involved. "This woman's on your side is she? How'd you swing that one?" he asked curiously. It was probably some foolish emotion on her part. Who cared about that kind of thing except where it was useful.
As for who he was, he smiled thinly at the realization. "Yes that's me, well sort of. I'm obviously not the same as the one in the books now am I? If nothing else I've got more style. But the genius mastermind description I'll take! And you can call me Moriarty." He liked it, how they refereed to him. He really was a criminal genius after all, and even if he wasn't a posh London oik with a Professorship. He didn't need it. He could have had a doctorate easily if he'd wanted but it had all been so boring. So very very dull.
"They'll always line up to hate people like us. That's how these people are. They'll never trust that we're not planning something, which, I suppose in my case is fair, since I usually am. But I was doing alright until Watson ratted me out. He's Sherlock's little live in pet, you know. And then Sherlock arrived and well... That's just been delightful, really."