The below image popped up just after I received a text message. Any ideas as to what it may be? Really just checking it's some kind of system error rather than a virus etc.
Thanks, Phil.
iPhone 4S, iOS 6.1.3
That is a service message from your cellular provider... or, at least, it's supposed to be. That looks like it could be an error in the cellular system. Unless it happens again, I wouldn't worry about it. If it does, some cellular providers have left their systems a bit too open, allowing third-parties to figure out how to send these kinds of messages, so you could be getting spammed by someone who knows how to do that.
Whatever the case, though, it's not a virus.
Double exclamation mark over text messages?
