NEWARK, N.J. —  Six more people pleaded guilty Thursday to operating a Web site that investigators claimed was one of the largest online centers for trafficking in stolen identity information and credit cards.

With others who pleaded guilty in recent weeks, that brings to 12 people who acknowledged roles with the site, http://www.shadowcrew.com, which had about 4,000 members who dealt with at least 1.5 million stolen credit card numbers and caused more than $4 million in losses, federal prosecutors said.

"The losses incurred were to the issuing banks and MasterCard, Visa, American Express, who reimbursed those who were victimized by these crimes," Assistant U.S. Attorney Kevin O'Dowd said.

Eight of those who pleaded guilty were among 19 in the United States and abroad who were indicted in October 2004 after federal agents gained control of the site during a yearlong undercover investigation by the Secret Service and other agencies. Of the remaining 11, five are fugitives and six still have charges pending.

The other four who pleaded guilty were among eight people charged by a federal complaint.

The site used techniques such as "phishing" and spamming to illegally obtain credit and bank card information, which were used to buy goods on the Internet.

Phishing scams use e-mails that appear to come from banks or other financial institutions to induce recipients to verify their accounts by typing personal details — credit card information, for example — into a Web site disguised to appear legitimate.