The I.R.S. scheme is still around. The I.R.S. lists impostor calls as one of its “dirty dozen” fraud risks. Kati Daffan, assistant director of the F.T.C.’s division of marketing practices, said it was not clear why Social Security-based calls were increasing. It may be that criminals are adapting their approach as the public becomes more aware of the fake income-tax calls.

“Scam artists are always changing to the next big thing,” Ms. Daffan said.

People filed over 76,000 reports about Social Security impostors in the 12 months ending in March, with reported losses of $19 million, according to the F.T.C., which investigates consumer fraud. About 36,000 of the complaints and $6.7 million of the losses were reported in February and March.

By comparison, the agency said, consumers reported $17 million in losses to the I.R.S. scam at its peak, during the 12 months that ended in September 2016. The data comes from the F.T.C.’s Consumer Sentinel Network database, a pool of millions of consumer complaints.

A typical loss for those who reveal their loss to the F.T.C. is about $1,500, the agency said.

In some cases, as with the I.R.S. calls, the criminals are quite aggressive and try to scare their targets into action. In one common tactic, the fake callers tell the potential victim that his or her Social Security number has been “suspended” because of suspicious activity or because it has been involved in a crime. The callers may ask their victims to confirm their Social Security numbers. They even say that the victims must withdraw cash from their bank accounts and that the accounts will be frozen if the victims don’t act quickly.

Some people are scared enough that they follow the caller’s orders to withdraw money and put it on a gift card, then give the card’s number to the criminals. Less commonly, the F.T.C. said, people have followed instructions to withdraw cash and convert it into a digital currency, by depositing it into a Bitcoin A.T.M., where it becomes accessible to the thieves.