Dan Clements, founder of Cardcops.com, a Malibu, Calif.-based company that enables consumers to check for stolen credit card numbers, said that the number of stolen credit cards and pieces of personally identifiable information appears to be growing. "There is a definite underground where you can buy and sell this stuff without the threat of law enforcement," he said.

Much of the stolen information appears to have been snagged through hacks into systems containing confidential data and from phishing scams, he said.

"Almost every day we see a new merchant being hacked" and information being stolen from their systems, said Clements, whose company scours known hacker sites, chat rooms and other online locations for stolen credit cards and personally identifiable bits of data.

Over the past three years, Cardcops has alerted more than 500 merchants about data compromises resulting from potential hacks into their systems. Clements said the company has also found more than 1 million stolen credit cards and between 7 million and 10 million pieces of personally identifiable information associated with those cards, such as last names and addresses, he said.

Most of the time, the merchants involved appeared unwilling to take responsibility for their security lapses, he said. "When you show them the data, they only fess up to what is put in front of them," Clements said.