An on-line invitation to buy stolen cellular telephone and credit card data led to the arrest of six people and the seizure of more than 20 computer systems, authorities said Monday.

During an eight-month investigation, an undercover Secret Service agent using the name “Carder One” and a confidential informant operated a private computer bulletin board system called “Celco 51,” authorities said.

Through the Internet, the undercover team advertised that Celco 51 catered to those involved in computer fraud, court papers said.

“What we really did was set up an old-fashioned ‘swag shop’ in cyberspace,” said Assistant U.S. Attorney Donna A. Krappa. A swag shop is where stolen goods are traded.

Two of the suspects were accused of conspiring to break into the computer system of McCaw Cellular in Portland, now AT&T Wireless. The others were accused of selling the numbers to people’s cellular phones.