John I've seen it happen. A forum I used to visit had a video game sub. We were discussing a game that was coming out soon and one of the testers ( let's say the Source ) was a member and giving some real good info on things that hadn't been released. Another poster, wanting to be Billy Big Balls ( we'll call him the ITK ), went on another gaming forum and posted some of the info. The publisher came after him (ITK) with lawyers, he said where he had got the info from, and they figured out who the tester (source) was and fired him.
Slightly different. The transfer market is so speculation and gossip heavy that it'd be impossible to trace a rumour. I could suggest that we were interested in a player that we haven't been linked with as of yet (say Lewandowski) and if the club were actually making moves to buy him, it'd be absurd to pursue to me to find my source.