City hackers have trained their guns on cellphone service providers. And more than one of them could be at work to make a point.

Six cellphone users have recently filed complaints with police about data stored in their handsets being accessed without authorisation. They have requested their cellphone service providers to provide more data security.

Each of the hacking victims received an SMS stating: “We have proved how unsafe your data is by accessing the server of your service provider without authorisation. We haven’t disclosed your personal details, including the text messages, to anyone. We have done it so that the service provider initiates security measures to protect their subscribers’ secrecy.”

Six months ago, Delhi police arrested Ankit Srivastava, 28, who had hacked into the database of a mobile phone service provider and obtain call details of over two dozen phones belonging to staff in the Prime Minister’s Office. Law enforcing agencies in the city fear that the hi-tech crimes here could be similar in nature.

“This is the latest trend in Calcutta’s crime world. We will hold talks with the cellphone service providers in this regard. Though our officers will also work on the cases, the service providers will have to do the main job,” said deputy commissioner (detective department) Gyanwant Singh.

The victims do not know what to do. Gariahat-resident Monideepa (name changed on request), a retired government employee, said she had received a packet by post containing details of the calls she had made or received on her phone and the contents of the text messages she had sent or received over the past four months.

“In a letter, the sender claimed that he had the personal data of other mobile users. I changed my cellphone number, but I am not sure whether that would help,” Monideepa added.

In a letter addressed to deputy inspector general (operations) of Criminal Investigation Department (CID) Rajeev Kumar, a bank employee said the hacker had accessed the text messages she had sent to her husband. She, too, received a letter from a hacker, who identified himself as Sanju Vaidyanathan.

In the letter, Vaidyanathan claimed that he is an “ethical hacker” and only wants to show how cellphone service providers are lax in protecting their clients’ data.