Recently, there have been some exploits on Android, and most recently, there was Stagefright. This is ones that allows you to remotely control your phone. Scary.
I found out about this from an app I have called Lookout, which is like a antivirus for the phone. It alerted me of this, started some workarounds, but really, you would need to get an update on Android to fix it. Coincidentally, I see an Android update. More specifically, a security update.
It updates, and then I check for Stagefright, and no longer vulnerable. Cool. That’s one of the benefits of Nexus, and that is they are the first ones with the latest Android update.