A Russian hacker has allegedly obtained and put for sale online the usernames and passwords of around 33 million Twitter users on Thursday. The account belonging to Evan Williams, co-founder and former CEO of the microblogging site, was also compromised for a brief time, reported IANS. A group called OurMine – one that had claimed to have accessed Facebook chief Mark Zuckerberg's social media accounts recently – took responsibility for hacking Williams' account.

However, Twitter denied any security breach, but said it would look into the matter. A company spokesperson said Twitter was confident that it had not been hacked. "We are confident that these usernames and credentials were not obtained by a Twitter data breach – our systems have not been breached," the company said.

Recently, LinkedIn and Myspace faced security breaches. Millions of passwords from both these websites were put up for sale on the dark web. Experts believe that using leaked LinkedIn and Myspace passwords on Twitter accounts is helped hackers access several celebrity Twitter accounts over the last week. Facebook CEO Mark Zuckerberg and singer Katy Perry are a few others whose accounts were hacked recently.