MANGALORE (India) • Waving a giant saffron flag, Mr Pranav Bhat last week joined a political rally for Prime Minister Narendra Modi and India's ruling party in Mangalore, the sweltering port city on the south-west coast.
Milling on a vast field with his college buddies, the 18-year-old cheered for Mr Modi and his Hindu-oriented Bharatiya Janata Party (BJP), which was trying to wrest control of Karnataka state from the more secular Congress party in legislative elections.
Yet the most intense political campaigning was not taking place on the streets but on WhatsApp, which has 250 million users in India.
More than any other social media platform, WhatsApp was used in recent months by political parties, religious activists and others to send messages and distribute news to Karnataka's 49 million voters.
Mr Bhat, a BJP youth leader, said he used WhatsApp to stay in constant touch with voters. He sent them critiques of the state government, dark warnings about Hindus being murdered by Muslims - including a debunked BJP claim that 23 activists were killed by Islamists - and jokes about Congress leaders.
His own WhatsApp stream was full of election updates. "Every minute, I'm getting a message," said Mr Bhat, a college student.
In the run-up to the May 12 vote in the state - results of which were announced yesterday - the BJP and Congress claimed to have set up at least 50,000 WhatsApp groups between them to spread their campaign messages.
At the same time, many others - identities unknown - distributed videos, audio clips, posts and false articles designed to widen the area's Hindu-Muslim fissures.
The role that WhatsApp plays in influencing voters has received far less attention than that of its sister services, Facebook and its photo-sharing platform, Instagram.
Unlike those, WhatsApp's messages are generally hidden because it began as a person-to-person communication tool. Yet it has features that make it a potential tinderbox for misinformation and misuse.
Users can remain anonymous, identified only by a phone number. Messages are forwarded with no hint of where they originated. And it is encrypted, making it impossible for law-enforcement officials or even WhatsApp to view what's being said.
Mr Govindraj Ethiraj, founder of Boom and IndiaSpend, two sites that fact-check Indian political and governmental claims, said WhatsApp was insidious in spreading false information. "You're dealing with ghosts," he said.
WhatsApp officials said they are concerned about misuse of the platform, whose terms of service forbid hate speech, threats of violence and false statements.