Bicycle lock maker Kryptonite, stung by revelations that some of its locks can be pried open with nothing more than the hull of a ballpoint pen, yesterday offered to provide free upgrades to customers who purchased the vulnerable locks.

The Canton, Mass., company, a division of Ingersoll-Rand, said it would offer new locks or parts to anyone who's purchased the following models within the last two years: Evolution, KryptoLok, New York Chain, New York Noose, Evolution Disc Lock, KryptoDisco or DFS Disc Lock. Customers will receive different types of upgrades depending on what style of lock they own.

The company said the exchange program will be administered through its dealers, but details of how customers can participate won't be made available until Wednesday when they will be posted on Kryptonite's Web site, according to a company statement.

In the meantime, area bike stores began informal exchange programs yesterday as concerned customers returned locks that until this week had been considered by many to be the gold standard for preventing theft.

"Quite frankly, Kryptonite's the most trusted name in the industry. For something like this to happen, it shook everybody," said Randy Walther, general manager of Revolution Cycles in Arlington. Walther said he was still waiting for word from Kryptonite on how the exchange would be conducted, but said recent customers who don't feel safe using the defective locks could bring them back to his shop.

City Bikes in Adams Morgan had exchanged about a dozen locks by late yesterday, and was expecting more over the weekend.

"You don't tell everyone in America how to steal something easily and expect it not to happen," said Shawn Smith, City Bikes' floor manager. "If people don't get their locks replaced, they're vulnerable to theft."

Word of the locks' vulnerability first circulated via a video on the Internet that showed a demonstration of how the hollow shaft of a Bic pen could be used in place of a key. Not all Kryptonite locks are vulnerable; those that are use a "tubular cylinder" design. A Kryptonite spokeswoman said that other types of products from companies that use tubular cylinder technology could also be subject to the flaw.

Smith said he didn't believe the security of a Kryptonite lock could be so easily breached until he tried for himself. "We did it a dozen times," he said. "It takes 30 seconds at most."

City Bikes is offering those who bought one of the locks at the store within the last year the chance to exchange it for a comparable lock, said Smith. The Kryptonites involved typically sell for between $30 and $55, he said.

"Just about everyone with a bike has one," Smith said. "They've been recommended highly for years."

Smith said City Bikes had ordered $20,000 worth of locks from a competing brand, OnGuard, in response to the problems with the Kryptonite locks. He said the store will stick with Kryptonite in the future as long as the company can prove its new locks aren't so easily penetrated.

"We'll stay with them," Smith said, "but they need to redesign their locks."

Bicyclists considered Kryptonite locks secure until a glaring flaw was exposed this week.Word spread quickly on the Internet that a ballpoint pen's plastic barrel could open Kryptonite locks.