Four Citigroup Inc executives who bought the bank's stock last week have already generated a $2.2 million paper profit, regulatory filings show.

The executives, including director Roberto Hernandez, benefited as the company's stock climbed 47 percent since March 10, when Chief Executive Officer Vikram Pandit said in a memo that the bank is having the best quarter since 2007. Their buying spree was the first by bank insiders since Jan 14, filings show.

"You're supposed to buy when everyone else is selling," said Bruce Foerster, a former Lehman Brothers Holdings Inc. managing director who now runs South Beach Capital Markets in Miami. Banks have internal systems to monitor executive trades and prevent abuses, he said.