It is illegal. Complaint can be filed against the said person for the offence of defamation. Both civil as well as criminal defamation case can be filed simultaneously. According to section 499 of IPC, whoever, by words either spoken or intended to be read, or by signs or by visible representations, makes or publishes any imputation concerning any person intending to harm, or knowing or having reason to believe that such imputation will harm, the reputation of such person, is said, except in the cases hereinafter expected, to defame that person. Maximum punishment for the offence of criminal defamation is 2 years. In a civil defamation case, a person who is defamed can move court and seek damages in the form of monetary compensation.

Also, complaint can be filed with the police under the provisions of section 66 if IT Act.

Depends on nature of comment. Not all kind of comments whether in public/private or through social media attract criminal offense.  

anything sent on what's app which harms the reputation can definitely come under purview of defamation (backed by S. 66 IT act and Indian evidence Act) Punishment is imprisonment up to 2 years or fine or both. 

issue legal notice to with draw false and defamatory statements made against you and tender unconditional apology 

2) file complaint of criminal defamation if accused refuses to with draw defamatory statements against you 

See you can serve the said person with legal notice of defamation and then on notice if he fail to give a public apology and damages.

You can file a suit for recovering damages and a complaint directly with magistrate for defamation.

Dear sir, 

If someone has published something derogatory to your reputation then the appropriate cause of action is to file a defamation case(either civil or criminal defemation). Apart from that it will be advisable to you that you send a legal notice stating to tender a written apology otherwise appropriate proceedings will be initiated against you. 

You can contact me for consultation and sending the legal notice. 

Regards, 

YUGANSHU SHARMA 

ADVOCATE 

Only IPC sections can be invoked including defamation case

Hello,

If you are a girl then IPC as well as it act will apply , otherwise the same will fall under the provision of it act 

Regards

Simple answer is no . Because posting a message in WhatsApp group can not be treated as an act of publication which is the vital element of defamation.

What is the derogatory comment that aggrieved you, if you consider the same as derogatory, then you may send a legal notice to the offender asking his explanation or else you can sue him under section 500 IPC

Take screen shot of messages. 

Send legal notice to sender for apology and compensation for damage.

If the person refuse to compensate file suit against him. 

Dear Sir,

Offensive WhatsApp posts can now land group administrator in jail

If any statement is made by a group member which is fake, can cause religious disharmony, or rumour, the group admin must deny it on the group and remove the member from the group, the order said.

"In the event of inaction from the group admin, he or she will be considered guilty and action will be taken against the group admin," it said.

Such a post must also be reported to the nearest police station so that action can be taken against the member under the law, it said.

The order, issued yesterday, says while freedom of expression on social media is important, it also comes with a responsibility.