The thieves operate from small offices in Toronto, Canada, and hangar-size rooms in India. Every night, working from lists of names and phone numbers, they called World War II veterans, retired schoolteachers and thousands of other elderly people and posed as government and insurance workers updating their files. Then, the criminals empty their victims’ bank accounts.

Telemarketing fraud, once limited to small-time thieves, has become a global criminal enterprise preying upon millions of elderly and other people every year. Vast databases of names and personal information, sold to thieves by large publicly traded companies, have put almost anyone within reach of fraudulent telemarketers. And major banks have made it possible for criminals to dip into victims’ accounts without their authorisation.

The banks and companies that sell such services often confront evidence that they are used for fraud. Although some companies have made refunds to victims who have complained, hardly any have stopped working with criminals even after executives were warned that they were aiding continuing crimes. Instead, those companies collected millions of dollars in fees from scam artists.

“Only one kind of customer wants to buy lists of seniors interested in lotteries and sweepstakes: criminals,” said Sgt Yves Leblanc of the Royal Canadian Mounted Police. “If someone advertises a list by saying it contains gullible or elderly people, it’s like putting out a sign saying ‘Thieves welcome here’.”