I am pasting the section 67 of the IT Act under which the gentleman in question has been taen into the police custody.It is funny.
Publishing of information which is obscene in electronic form. - Whoever publishes or transmits or causes to be published in the electronic form, any material which is lascivious or appeal to the prurient interest or if its effect is such as to tend to deprave and corrupt persons who are likely, having regard to all relevant circumstances, to read, see or hear the matter contained or embodied in it, shall be punished on first conviction with imprisonment of either description for a term which may extend to five years and with fine which may extend to one lakh rupees and in the event of a second or subsequent conviction with imprisonment of either description for a term which may extend to ten years and also with fine which may extend to two lakh rupees.

Thanks @shivangi for letting us know what is the legal stand rather than wasting time and energy debating over a never-ending issue ! But i have some contradictory view from urs..... This time it was just Sonia Gandhi... what would have been the scenario had it been about , say from instance, about Mother Teresa or for that matter Mahatma Gandhi? Dont u think they should be restrained from airing such derogatory view?