Millions of web users are being asked to reset their passwords as concerns spread over a major hacking attack.
Yahoo, Twitter and LinkedIn have asked users to change their details, days after gossip site Gawker was hacked.
Online game World of Warcraft, which has more than 12 million subscribers, has also asked some users to reset their passwords.
Blizzard, the company behind the game, said it was an attempt to "minimise the effects" of the Gawker breach.
Although thousands of Twitter accounts were compromised after the attack, there have been few other reports of damage directly linked to the breach.
Many companies, however, have taken steps to identify users at risk and warn them before an exploit can take place. A spokesman for LinkedIn said it necessary to take "proactive security measures" to screen users thought to be in danger.
