How do you respond when someone asks, "How much is your salary?"

I asked this question multiple times and was always taken aback by the person's audacity, but my response was always the same:

What is your annual salary?

"Secret"

After this response, no one has asked me this question again, because I believe that everyone understands that it is a highly private and improper question, although curiosity may push some to ask them to see if they can obtain an answer.

Additional information and disclaimer*****: Some of the brothers and sisters seem to have misunderstood my response, therefore I'd like to clarify:

Of course, when this question is asked in order to compare my work salary to the average salary of others in the labour market, there is no problem.... When a buddy in the field of work asks me for assistance, it's for a good reason.... These arguments are obvious and self-evident, and they are, of course, non-intrusive. Because there are multiple comments on this topic, I realised that my answer might not be apparent to some.The only time I'd answer this question personally is if it's out of sheer intrusion...and for the sole purpose of gathering information out of curiosity, not for any advantage or benefit at all. What are your husband's and siblings' salaries? For example, why hasn't your sister married yet? When will you have another child, and what are you waiting for? Etc. from a plethora of meaningless private queries, and this was my goal in responding to them.

Questioner who, according to my interpretation of the question, does not want to share his pay and is seeking guidance on how he should react to the questioner.

I appreciate everyone's useful and diverse perspectives on the matter in general... I hope that I have clarified the answer.