A previously unknown hacker group has posted online the details of 450,000 user accounts and passwords it claims to have taken from a Yahoo server. The Ars Technica technology news website reported that the group, which calls itself D33DS Company, hacked into an unidentified subdomain of Yahoo's website where they retrieved unencrypted account details.

A Yahoo spokesperson in Singapore declined to comment.

The affected accounts appeared to belong to a voice-over-Internet-protocol, or VOIP, service called Yahoo Voices, which runs on Yahoo's instant messenger. The Voices service is powered by Jajah, a VOIP platform that was bought by Telefonica Europe BV in 2010.

The hackers' website where the original claim was made, d33ds.co, was not available later on Thursday. It was registered in February. Industry website CNET reported the hackers as saying the breach was intended as a "wake-up call and not as a threat" and that Yahoo's security was lax.

The Voices hack is one of several in recent months. The business networking service LinkedIn admitted last month that 6.4 million member passwords had been stolen from its website