Hundreds of domain names resembling well known names and trademarks have been registered by fast thinking Web users who spotted a glitch in the registration system.

Domains including 'microsoft-.com', 'aol-.com' and 'computers-.com' were registered in the last month at four of the 23 registrars worldwide that provide the domains.

But the domain owners are going to have to surrender their names, which either start or finish with a hyphen, because the hyphen causes technical problems with some Internet software, such as FTP, Telnet, Traceroute and Ping.

Network Solutions (NSI), the registry which logs all top-level domain names - such as .com, .net and .org - said 845 of these domains have been recorded. NSI discovered the loophole on 3 January and has since placed a filter on its system preventing further similar registrations.

A spokseman for NSI said it is up to the registrars, which include San Francisco based Internet Domain Registrars and Baltimore based Alabanza, to reimburse their customers for the invalid names.

"We've informed the registries that they are in violation, and it's up to them to decide what to do," an NSI spokesman told vnunet.com. NSI will refund the $9 it charges registries to accept these registrations.

The domain name registration system has evolved slowly since the US government ended NSI's monopoly as the sole registrar of top level domains last year. This latest incident drew harsh criticism from some registrars.

"This is a classic example of the nonsense in the new distributed registrar and registry system," said Ivan Pope, chief executive of UK registrar Netnames.

"NSI is claiming it is down to new registrars to filter out these domains - this is fairly preposterous. If there are fundamental rules about what is not a domain name and all registrations end up at the registry, surely the rules should be made at the registry end," said Pope.

But Phil Callan, managing director of Network Solutions UK, NSI's registrar arm, put the blame on new entrants into the registration business. "I understand that some of the newer registries hadn't read their contracts properly," he said.

Neither Network Solutions UK nor Netnames registered any top level domains beginning or ending with hyphens.

"We wouldn't process them, basically," said Pope. "It's an illegal positioning of a character, the same way as if you tried to put a & or ? in. The staff would not bother to put these registrations through."

Pope said it would also not be possible to register .co.uk domains using the same trick. "There is a rule set implemented by the technology that processes applications to prevent that," he said.

There are 12.9 million domain names registered worldwide.