If you have a Yahoo account, you may want to think about changing your password.A group of hackers has stolen the usernames and passwords of more than 450,000 Yahoo users and posted them to a public website.The affected accounts appear to belong to customers of the company’s VOIP (voice-over-internet-protocol) service called Yahoo Voices, which runs on Yahoo’s instant messenger.The hacker group, which calls itself D33DS hacked into one of Yahoo’s servers where they obtained the encrypted information and posted it online at d33ds.co. 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."We are fixing the vulnerability that led to the disclosure of this data, changing the passwords of the affected Yahoo users and notifying the companies whose users accounts may have been compromised," said company spokeswoman Dana Lengkeek.The impact stretches beyond Yahoo though because Yahoo Voices allows users to log in with login details from other sites — which means that user names and passwords for Yahoo, Google Gmail and Microsoft Hotmail/Windows Live, AOL and many other e-mail hosts were among those posted publicly on the hacker forum.Yahoo’s interim CEO, Ross Levinsohn, faced tough questioning from frustrated shareholders in the embattled internet company’s annual meeting yesterday. The seven shareholders who grilled Mr Levinson made it clear they are losing their patience with the company.Mr Levinsohn stepped in two months ago when the company fired Scott Thompson as CEO for allegedly lying on his resume. Mr Thompson was on the job just four months — taking over when Yahoo fired Carol Bartz as CEO. Mr Levinsohn is now considered to be the leading candidate to be named permanent CEO.The Yahoo hack comes just a month after millions of passwords were stolen from several sites. 6.4 million passwords were stolen from business networking site, LinkedIn and within 24 hours of that data breach, 8 million passwords were stolen from Last.fm and 1.5 million were taken off of dating site, eHarmony. In May, 60,000 Twitter usernames and passwords were also leaked.Just like in previous breaches, the vast majority of the Yahoo accounts that were hacked had predictable passwords. Security firm Eset has analysed the data released in this latest hack and says a number of the exposed passwords were all too easy for hackers to guess. The top ten passwords used included “123456”, “password”, “welcome”, “ninja”, “abc123”, “123456789”, “12345678”, “sunshine”, “princess”, and “qwerty”. However, even some more complicated passwords like “rpfbkxdv13” were hacked as well.It’s unclear why Yahoo Voices was storing unencrypted passwords in its back end database.If you're a Yahoo Voices user, you should change your password soon, and if you use the same login credentials on more sensitive services such as e-mail or financial accounts, you should also change those as soon as possible.