Re: The Avengers 2! The Official News and Speculation Thread - Upgrade section 4
Thinking about it... Joss' comments on how the current team affect Ultron and how it changes makes me think that Hank could have created Ultron and that it has been a thing for a while now, he's just not in the movie. Then the team manage to do something to it (perhaps something to do with Scarlet Witch and Quicksilver? Joss said they'd be causing trouble) that makes it go rogue...
"I'm Ant-Man... What, you haven't heard of me?"
- Scott Lang / Ant-Man