Got someone else's details on my iPad, need help quick

Ok, I really need help, I work on my new iPad 3 a lot, and my contacts mean a lot to me, but today I opened up my contacts and found names and numbers that i had never seen before in my life, then I opened up the photo stream and realised some girls Random Pictures had turned up...I don't want anything to do with this other persons information. And I don't want them having the ability to access mine, as it is important and private... Why is this happening, why is someone else information merging onto my device, I need immediate help as I'm loosing valuable time. Many thanks.