^ Generally, almost all Government Departments ignore anonymous tips because most of the anonymous tips are given just to divert the focus of the officials. But if you could provide some rock solid proofs of an illegal activity, they might enquire about it first before taking any adverse action on the culprit. By that time, these is chance for leakage of information too. So it's best to provide the information to your friend who is working in Income Tax Department and ask him to protect your identity rather than sending anonymous tips. This is the best approach, if you trust him. If you don't trust him, it's better to send anonymous letters.
He is the one suggested me too keep my identity anonymous while reporting but if you want do at your own risk he said.Income tax doesn't have severe punishment for this,only they might seize the assets if there is no proof for source of income but how can we get them jailed.They are doing illegal things and living like they can do what they want and can manage anything with the money.
But as Indian citizen its hard to digest that .
. If you provide the tip your privacy will be kept as a secret unless you are weeding out any politician or someone with power 
.