iPhone Device name changed on its own...

I was recently out of the country and when I returned I noticed that my iPhone device name changed from my personalized one to iPhone (70).... I hope this doesn't mean I've been hacked... what do I need to do to be sure everything is ok??? How do I see if my phone was accessed elsewhere? Should I change my apple id password? Thanks for any suggestions! One more thing -- is there a recommended virus scan for an iPhone?