Twitter has confirmed that hackers may have gained access to information on 250,000 of its more than 200m active users.
The social media giant said in a blog posting that earlier this week it detected attempts to gain access to its user data.
It shut down one attack moments after it was detected.
Twitter discovered that the attackers may have stolen user names, email addresses and encrypted passwords belonging to 250,000 users.
The company said they could not comment specifically on whether Irish accounts were affected by the hacking incident.
It said that "the blog post does say that we felt it was important to publicise this attack while we still gather information".
Twitter reset the passwords and sent emails advising affected users.
The online attack comes on the heels of recent hacks into the computer systems of US media and technology companies, including The New York Times and The Wall Street Journal.
Both newspapers reported this week that their computer systems had been infiltrated by China-based hackers, likely to monitor media coverage the Chinese government deems important.
China has been accused of mounting a widespread, aggressive cyber-spying campaign for several years, trying to steal classified information and corporate secrets and to intimidate critics.
The Chinese foreign ministry could not be reached for comment, but the Chinese government has said those accusations are baseless and that China itself is a victim of cyber-attacks.
"Chinese law forbids hacking and any other actions that damage Internet security," the Chinese Defense Ministry recently said.
"The Chinese military has never supported any hacking activities."
Although Twitter said in its blog that the attack "was not the work of amateurs, and we do not believe it was an isolated incident."
"The attackers were extremely sophisticated, and we believe other companies and organisations have also been recently similarly attacked," the blog said.
"For that reason we felt that it was important to publicise this attack while we still gather information, and we are helping government and federal law enforcement in their effort to find and prosecute these attackers to make the Internet safer for all users."
In a telephone interview yesterday, Mr Soltani said that the relatively small number of users affected suggested either that attackers weren't on the network long or that they were only able to compromise a subset of the company's servers.
Twitter is generally used to broadcast messages to the public, so the hacking might not immediately have yielded any important secrets.
But the stolen credentials could be used to eavesdrop on private messages or track which Internet address a user is posting from.
That might be useful, for example, for an authoritarian regime trying to keep tabs on a journalist's movements.