BANGALORE - Screenwriter Kavita (name changed) in Mumbai's Hindi film industry has never been more nervous about what she says on WhatsApp. She has deleted old chats saved online, cancelled fresh back-ups, and is gradually moving to Signal, another messaging app that she feels is more secure.

"I have sanitised as much as I can," she said.

In the last month, there has been panicked conversation among many smartphone users in India about digital privacy, as they see how easily the police have accessed personal phone data in a much-publicised probe into drug use in Bollywood, and in other parts of the country, used chats to build cases against human rights activists and critics of the government.

Following the possible suicide of young actor Sushant Singh Rajput on June 14, agencies investigating the alleged role of his actor-girlfriend Rhea Chakraborty claimed they had found mentions of drugs in her WhatsApp chats with other people.

In a case probing "a drug citadel" in Bollywood, India's narcotics control bureau has since arrested 20 and questioned 35 people, including popular actors like Deepika Padukone and Sara Ali Khan and their publicity managers.

Those who are called to the agency's office often have to submit their phones, from which backed-up chats and details can be accessed. The agency has said that any chats about drugs have led to more people being summoned for questioning. Some news channels have repeatedly telecast leaked screenshots of some of these chats.

"Drug involvement can destroy careers. Which means everything will have to be furtive now," said Ms Kavita.

India's drug laws criminalise the consumption, possession and sale of many drugs. In the past month, many in Mumbai have been arrested based on their phone texts.

In Delhi, the special cell investigating February's religious riots that killed 53 people focused on a WhatsApp group called Delhi Protest Support Group.

The group has about 100 members including social activists, prominent documentary filmmakers, teachers and students who participated in the protests against discriminatory amendments to India's citizenship law.

The police summoned and questioned several members of the WhatsApp group over three months. Holding that the riots were the product of a "large-scale conspiracy" by "professional ideological deviants" opposed to the citizenship law, the police have charged 15 protesters with inciting riots.

"It's clear that the police are just targeting people who have dissented against the government," said a Delhi-based artist who was a member of the WhatsApp group, but was not charged.

Another young artist said: "It is surreal how easily the state can access your private chats. Many of us are actively trying to shift to Signal app because it has the disappearing messages feature. It's not been easy because we are habituated to WhatsApp."

In June, the Delhi police also charged 11 members of WhatsApp group Hindu Kattar Ekta (Militant Hindu Unity) who they said exchanged messages to mobilise crowds to kill Muslims.

A Bangalore social activist said that college students detained in January while protesting against the citizenship laws received police threats that their chats on sex or dating would be shown to their parents.

"Two students were held at a police station when they went to help another young person. The police made them unlock their WhatsApp and e-mail. One guy never got his phone back. He went off social media after that," said the activist who then deleted her own chats with the student and moved to Signal.

Responding to the growing concerns, a WhatsApp spokesman clarified in a statement on Sept 25 that messages on its application have end-to-end encryption "so that only you and the person you're communicating with can read what is sent".

But the company encouraged people to use strong passwords or biometric IDs to prevent third parties from accessing content stored on their devices.

Indian newspapers and tech experts have been offering tips on how to delete back-ups of chats, and explaining what encryption is and what digital rights Indians have.

India's privacy law has been in draft stage for a decade now. Meanwhile, the Indian criminal justice system allows searches and seizures of personal devices without warrants. When asked by the police for his password, a person is required to answer truthfully.

Privacy advocates say that access to a person's phone or laptop is usually unlimited, and may even extend through social media to people who are not under investigation and have not consented to part with their data.

The Internet Freedom Foundation, a privacy rights non-profit group, recommends that judicial authorisation be mandatory for searches of personal devices.