The allure of WhatsApp, the mobile messaging application owned by Facebook, is that it is free, simple to use and encrypted end-to-end. Researchers have found that 66 percent of the 180 million internet users in urban India and 85 percent of rural Indians regularly use the internet for access to social media. India has about 300 million smartphones now, a significant portion being very cheap and made in China. About 200 million of WhatsApp’s one billion users are in India, making the country the app’s biggest market.

On New Year’s Eve, 14 billion messages were exchanged on WhatsApp in India, according to data released by the service. WhatsApp rolled out the video-calling feature for India in November 2016. Indians have made over 50 million minutes of video calls every day using WhatsApp since then, more calls than from any other country.

The gifts of free usage and anonymity have made WhatsApp the most popular tool to spread both outlandish stories and politically motivated rumors. On an ordinary Indian morning, messages on the app can include the rumor of a popular mango drink being laced with H.I.V.-positive blood, the United Nations Educational Scientific and Cultural Organization’s rating of Narendra Modi as the best prime minister in the world or Julian Assange describing him as an incorruptible leader.

WhatsApp forwards are deftly tailored toward target audiences. Last year, the Indian middle class debated for weeks whether new 2000 rupee bills introduced by the Indian government after demonetization featured a chip that could be used to track the bills. There was no chip, but the rumor lived for a while.

Nationalist rage, often with sectarian overtones, dominates the world of India’s WhatsApp messages. One of the most popular WhatsApp hoaxes of this year featured the purported beheading of two Indian soldiers by Pakistani soldiers with a chain saw and a knife. India’s national song played in the background.

Pankaj Jain, who runs Hoax Slayer, a website that debunks fake viral stories on social media, found it to be a Mexican gang war murder video. “Almost 80 percent of the misinformation comes from right-wing groups and just spreads like wildfire,” Mr. Jain said.