Disclosing you salary details to anybody is "unethical".
Then why does HR (from well reputed companies too) ask for your last months salary slip's copy when you are planning to join their company?
I took panga and asked this question to one of these pious company's HR director. His response:
1. Although we always pay you based on our company standards we want to understand the market trends!
2. We want to make sure that you are a genuine employee!
3. Education is the manifestation of the perfection already in man (read "I want to confuse you").
ha ha ha ha