The blunder, described by lawyers as breach of fundamental data protection principles, has angered UK organisations which fear their e-mail addresses will be hijacked by marketing companies and spammers.
"This is not a very clever thing for any company to do. It is not a great advertisement. There are technical solutions to avoid doing this sort thing," said Dai Davis, lawyer at Nabarro Nathanson.
The case illustrates how easy it is for staff to misdirect internal e-mails which can embarrass or damage their employers when made public, unless safeguards are in place.
Tim Moore, director of network management specialist Parallel, one of the businesses affected by the blunder, said he was concerned his company would become a target for spammers.
"My first reaction was one of amusement. Then I realised my name was on the list and it had probably been sent to everyone else on the list," he said.
Network Solutions confirmed it had accidentally sent out a file containing a list of customers with .org websites to "a few thousand" customers as part of notification informing customers about changes in their registration.
"This was a mistake and we apologise for including those additional e-mails in the notification. The notification contained no other information from customers," it said.
Lawyers said that although the mistake breached data protection principles, which require information to be held securely and processed fairly, it would be difficult for organisations to prove they had suffered from the incident.
Companies would need to show they were receiving spam as a result of the list being published. This would be difficult if they were receiving spam e-mail anyway, he said.
"I would like to offer some strong words to Network Solutions," said Moore. "You hear a lot about security from Network Solutions. It needs to tidy up its own house first before it tells other people what to do."
Directors face 'cyber liabilities' >>