Yes it is a very service. It can be used for safe shopping on Internet, say you want to pay someone Rs 100 simply make a new Card of Rs 100 and use that Card...rather than giving the Real Card info.
More Info here
*www.hdfcbank.com/personal/payments/netsafe.htm
*netsafe.hdfcbank.com/ACSWeb/enrolljsp/netsafe.jsp
BTW, google is ur friend