Salary information is part of the negotiation for the job. Learn to negotiate and how to answer the question without answering the question.
Read "Ask The Headhunter's" articles/columns on salary negotiation for some background information.
If you say too large of number, you won't be hired. If you say too low of number, then you either leave $$$ on the table or they wonder why your number is low.
I've asked "are you offering me the job?" If they say no, then I ask if we can continue to see if I fit. This did not always work well.
Someone on HN posted the link to the Noel Smith-Wenkle method which is a better method and it works well, I've used it more than once effectively.