A director of a south Delhi-based security services firm lost Rs 50 lakh to cybercrooks, who diverted the money by repeatedly giving him blank and missed calls on his cellphone. Interestingly, they did not ask for any OTP.

The victim received a flurry of calls between 7pm and 8.45pm a few days ago. He picked up a few but ignored others as nobody spoke on the other side. He checked his phone only to see messages of RTGS (instant fund transfer) transactions worth nearly half a crore.

Initial inquiry revealed about Rs 12 lakh were transferred to one Bhaskar Mandal’s account while Rs 4.6 lakh went to one Avijit Giri’s account. Close to Rs 10 lakh each went into two other accounts. There were other transactions of smaller amounts too.

Probe suggests that masterminds of this con might be based in Jamtara area of Jharkhand while the recipients could be just the account holders who may have provided their accounts on rent to the scammers for a commission.

This case is one of the biggest cons reported from the capital in terms of money siphoned from an individual by cyber criminals, a source said. Generally, crooks siphon small amounts limited to thousands, given restrictions involving banks. However, the accused got lucky as the victim had a current account which enabled huge transactions without any hitches.

However, what is surprising is that the victim didn’t have to divulge any information to the crooks who pulled off the heist through just calls. Cops suspect the scammers may have used the “SIM swap” technique. Officials said it was a kind of account takeover fraud that generally targeted a loophole in the two-factor authentication or two-step verification in which the second factor is either a text message or call placed to a mobile phone.

“In this fraud, scammers also contact people’s mobile phone carriers and trick them into activating a SIM card. Once this happens, they take control over the phone,” said an officer.

“The crooks may also have been listening to the OTPs on phone through a parallel call initiated by them during the transaction. However, other angles, including a phone hijack, are also being probed,” another officer said.

The digital thugs seem to have targeted people across the country using this relatively new modus operandi. A chemical businessman and another person in Ahmedabad lost about Rs 64.4 lakh to crooks after getting missed calls in January this year.

A few months ago, a Mumbai-based textile businessman lost around Rs 1.8 crore from his account after receiving six missed calls on his phone. The money was stolen in 28 transactions across 14 bank accounts by the conmen.