So when the time came to gear up for Karnataka’s state elections, the parties turned to the same WhatsApp playbook.
“WhatsApp works like a nuclear chain reaction,” said Randeep Singh Surjewala, the Congress party’s chief spokesman.
U.T. Khader, an incumbent member of Karnataka’s legislative assembly, experienced the WhatsApp effect firsthand. Just before the election, Mr. Khader, a Muslim in the Congress party, was the target of what Mangalore police said was a disturbing new type of WhatsApp attack: a series of profane audio messages purporting to be an escalating exchange of threats between Hindus and Muslims over his candidacy.
In one recording, which was supposedly a phone call between two Hindu political activists, one voice harangued the other for putting a saffron-colored shawl, which the B.J.P. views as a Hindu symbol, around Mr. Khader.
“Why did you put a saffron shawl on Khader? Do you love your life or not?” the first voice said. “If I shove a knife into you, do you think Khader will come to your support?”
Later messages sounded like they came from Muslims threatening to kill the first voice in response. “Son of a prostitute, I’m warning you,” said one. “I’ll take you out.” The messages were sent to various WhatsApp groups, so they were heard by many voters.
Mr. Khader, who has represented the area for more than a decade and won with a large margin last time, said the alleged conversations were fake and recorded in a studio.