Droid adding unknown contacts.

[TripleJ]

I had an interesting problem earlier today and couldn't find any answers while searching on the web so i came here. I attempted to send a text message to a friend of mine, I selected his name from my contacts list, sent my message, and the response i got back was "Who is this?". As it turns out, the person I had sent the message to was not my friend but someone I had never met. A random number was added to my contacts list under the name of one of my previous contacts. Anyone have any idea how this happened without anyone tampering with my phone? Because i know that is not the case.