General badness

My Gmail account sent spam messages to everyone in my address book at 5am today (UK time). The password wasn't changed and I still had access to the account, so I just logged in and changed all the security settings. Then I started changing passwords on everything else, just in case. Since then the browser has become almost completely unresponsive and Google Maps crashes every time I open it. Commonsense says my phone is just struggling with weak signal in the stormy weather, but I'm concerned that I might have a phone virus. I wouldn't even know where to start with fixing such a thing.