Indian police are investigating the reporter behind a story on alleged leaks from a government database containing the personal details of more than a billion people, sparking accusations of media censorship.

Police said on Monday they were investigating a complaint of cheating, forgery and impersonation against the journalist, who reported last week that it was possible to buy information in the Aadhaar database for just Rs500.

Aadhaar is a controversial government scheme that uses fingerprints and iris scans to provide users a unique identity number they can use to access government and other services.

It was intended to reduce official corruption, but critics say it violates citizens' right to privacy.

The Unique Identification Authority of India, which administers the government identity card scheme, has denied any security breach but complained to police over the sting.

A police report documenting the complaint names the reporter, Rachna Khaira, as well as her newspaper The Tribune and “unknown persons” behind the alleged data leak.

The Editors' Guild of India said the criminal investigation amounted to an attack on press freedom.

“It is clearly meant to browbeat a journalist whose investigation on the matter was of great public interest,” it said in a statement.

Harish Khare, Tribune's editor-in-chief, said he stood by the report and regretted that the authorities had “misconceived an honest journalistic enterprise”.

Aadhaar was set up as a voluntary scheme, but has in recent years become compulsory for a growing number of services, including opening a bank account and paying taxes.

Opponents say that its use for what are effectively essential services means their right to privacy is being violated.

There have also been concerns about leaks, but the government has always maintained the system was secure.