In reply to stella1:
You are right to be concerned. The problem is by raising questions you could loose your chance of a job at either place.
If there's a 3rd party recruiter involved, then this may be how the information is changing hands, so double check terms and conditions as to what you have granted permission for them to do with your data. If however it's someone at the offering company who has a mate in the first company to offer, then from a company point of view that "mate" should be out of the company asap - they've essentially given your preferred company an advantage at a cost to their own (assuming you are a decent employee!).
This is an obvious tactic to employ you for less money than they may otherwise have offered... if they had asked you what the offer was, that's entirely different.
To be honest if you are happy with the offer and the company then take the job, but go and have a word with the data protection officer and HR afterwards.
Alternatively if you have (or can gather enough) evidence and you are so minded then you could take this a lot further