The offense? Printing a customer's complete credit card number and expiration date on receipts during sales transactions.

Since the beginning of the year, the state of California has required merchants to "truncate" or display only the last few digits on any printed receipts. But many small businesses are still unaware of the law and continue to issue statements with the whole number and expiration date.

Nassi, the director of the Town of Los Gatos Chamber of Commerce, was changing the Chamber's bank service last month when she learned of the new regulation. The Chamber was using an old credit-card processor that did not truncate the card number, but Nassi upgraded the machine as soon as she learned of the law.

"Had we not switched banks, we would have probably not known," she said.

The measure is intended primarily to protect consumers against fraud. Thieves can easily purchase goods or make new cards with access to someone else's credit data, said Joanne McNabb, chief of the California Office of Privacy Protection.

"Unfortunately, the kind of equipment that you need to create false documents and cards is readily available," she said.

Although the office of privacy protection is trying to inform business owners of the new law, compliance ultimately falls on the shoulders of the business owner. However, the office is looking to credit-card-system providers to inform their customers of the code and help them upgrade their machines.

"Here's who really should be doing it: the companies that produce that equipment," McNabb said.

Michelle Graff, vice president of marketing at Nova Information Systems, said that although Nova is not required to do so, the company has been diligent about asking customers to comply with the new regulations. Nova sent out a letter to notify customers of the change and also included a photo illustration with the letter, showing clients the difference between a truncated number and a full number on a receipt.

Nova serves more than 600,000 small businesses across the country.

Ellen Wayker, who owns a pet store on N. Santa Cruz Avenue, received a letter from Visa in the mail last December with instructions on how to change her machine. Compliance was simple, Wayker said, with the credit-card company walking her through the process.

Upgrading the machines is a generally straightforward process and doesn't take more than a few minutes. Graff said that for most Nova machines, simply updating the software can achieve the desired result. Customers can use their machines to dial Nova and upgrade their machines over that connection.

Despite the ease of compliance, Graff recommended that merchants with older machines take the opportunity to purchase new equipment, which often make transactions faster, quieter and easier. Newer terminals will also automatically truncate credit-card numbers on the printout; as mandated by state law, all terminals sold after January 2001 must have that function built in.

Not all businesses are required to change their machines. Those like Maria's Antiques on N. Santa Cruz Avenue, which do not print an electronic receipt but either record the number by imprint or handwriting, may still display the card's full details. Maria's Antiques uses an older machine with carbon-copy imprint.

"We want to give our customers the feeling of an antique store. So we keep the machine that way," said manager Deborah Armstrong.

Still, there are compelling reasons for business owners to comply with the new codes. If a customer complains of a violation, a merchant could be held liable for any damages incurred.

"In practice, the thing to do is get them to do it right," said McNabb.

Reporter Grant Shellen contributed
to this story.