The representative said the Internet service provider first noticed the error this morning. The company had been undergoing a routine test of its software when it accidentally sent a clearance code to credit card clearinghouses that pre-authorized the charges.
Microsoft does not know how many subscribers were hit, but the representative said the company so far had received more than 1,000 calls complaining of the surcharges.
One MSN Internet Access customer discovered a $504 charge from the service. Debi Judd of Moor Park, Calif., said the false charge had overdrawn her account.
The Microsoft representative said the company will reimburse the faulty charges and offer subscribers a free month of Internet access on MSN.
"Microsoft is working with financial institutions to make sure this pre-authorization is reversed," the representative said.
Nevertheless, Judd has a sour taste in her mouth from the incident. She's contemplating whether to cancel her subscription to the ISP.
"I'm going to reserve my decision to do (business) with them based on how their customer service handles this," Judd said. "But I'm not happy that that could happen."
MSN subscribers who were affected can call a service number (800-386-5550) if they suspect they were victims of the glitch. The billing error was first reported on MSNBC.com.