GASTONIA, N.C. — Gaston County government e-mails have been blacklisted after hackers used them to spread viruses, authorities said.

A breach in security caused several entities to block e-mail coming from Gaston County government addresses, effectively blacklisting them, said county computer network officials.

The city of Gastonia, the state of North Carolina and America Online all blocked county government e-mails. The Internet also lists the county's addresses as dangerous.

"This happens to a lot of businesses," said Sheila Courtney, the county's interim director of information technology. "Companies have to protect themselves, so they place suspect e-mails on spam lists or blacklist them."

People using the e-mail from one of the servers that blacklisted the county can send e-mail to the Gaston addresses, but the county cannot send messages back to them.

Computer hackers apparently obtained e-mail addresses from the county's server and used them to spread viruses, a method Courtney said was called "spoofing."

"We have to call all of these entities and explain to them that we are a legitimate government agency and that we need to be taken off of the list," Courtney said. "Some of them won't do it unless they can verify who you are."

The e-mail problem caused more frustration than real problems, Assistant County Manager Bill Beasley said. AOL's decision to block Gaston County e-mail created the biggest hassle because so many use that service, Beasley said.

To get the e-mail addresses off of the blacklists, the county's provider must have a service called reverse lookup, which allows e-mail recipients to confirm its source and whether it contains harmful viruses. The current provider doesn't offer reverse lookup, leaving Gaston County in a lurch until a new Internet provider can be chosen, Courtney said.