MUMBAI (Reuters) - Tanu had marvelled at her first smartphone when her Indian migrant worker husband gave it to her last November so the couple could stay connected. Before long, she was uploading pictures on Facebook and sending messages on WhatsApp.
Then a stranger sent her a Facebook friend request.
Tanu accepted, and when her new friend messaged her with promises of a better life she believed him, agreeing to a meeting that would ultimately lead to her being sex trafficked to the southern Indian city of Hyderabad.
"He did not touch me. He just handed me over to other people," said Tanu, 21, whose full name cannot be used for legal reasons.
"I did not fear anything while using the phone," she told the Thomson Reuters Foundation by phone on Thursday from the southern state of Kerala, from where she was rescued last week.
"I did not even know I had to fear getting trapped. I never thought something like this would happen." Police and campaigners in India say sex traffickers are increasingly using WhatsApp and Facebook to communicate with potential victims, calling it an invisible crime.
India's mobile phone users have multiplied on the back of cheap devices and data packs and the country is among the top data consumers in the world, with about a billion wireless connections.
That and free Wi-Fi in public places are making it easier for traffickers to operate - and harder for the authorities to track them down.
"These cases are emerging nearly every day, particularly of girls from the most vulnerable, remote parts of the country who have no exposure to city life," said Robin Hibu, joint commissioner with Delhi police.
Hibu spearheaded an anti-trafficking drive last year and handled the case of a girl from the remote northeastern state of Arunachal Pradesh who had befriended a man on Facebook.
He bought her an air ticket to Mumbai, where he sold her into a brothel.
"She was a high school student, very poor. But she had a smartphone with internet. This is a hidden tsunami. Today mobile phones are not that costly," said Hibu.
India is only the latest country to experience the grim phenomenon - all over the world, concern is growing over the use of technology by traffickers, who use social media to contact vulnerable teenagers before selling them into sex work.
But with Internet penetration at just 18 per cent in rural areas, according to a report from the Internet and Mobile Association of India, there is still huge scope for growth.
The report said mobile Internet was predominantly used by young people, with 46 per cent of urban users and 57 per cent of rural users under the age of 25.
Payments too have gone online, eliminating the money trail, according to Cassandra Fernandes of anti-trafficking charity International Justice Mission.
"Earlier, traffickers visited the family, convinced them about a job prospect in the city... they were usually people the family trusted," said Vivian Isaac, programme director of the My Choices Foundation which works with women and girls.
"Now they sit in their rooms and send messages on Facebook and WhatsApp and girls walk into their trap themselves. They never show hurry. They do it gradually, systematically." For families of migrant workers, the mobile phone is their only connection to their loved one.
Tanu now plans to change her number - but says she will keep her smartphone.