The relaunch of Sony’s PlayStation Network (PSN) has been delayed to a future date.

The Japanese electronics company had earlier said that some of its services would be restored by the weekend. However, Sony has said that it will carry out its promise to restart the services fully by 31 May.

Last month Sony suffered one of the biggest security breaches in history which is believed to have compromised sensitive details of about 100 million people worldwide. The company shutdown its services on 19 April.

Sony said it will not restore services until it is sure that the service is protected against future attacks.

"We were unaware of the extent of the attack on Sony Online Entertainment servers, and we are taking this opportunity to conduct further testing," Sony said in a blog.

"We won’t restore the services until we can test the system’s strength in these respects."

A Sony spokesman Shigenori Yoshida told Bloomberg that the company is uncertain of the date when it will resume the services.

In a related development, Sony has written a letter to Connecticut Senator Richard Blumenthal, to defend against allegations that it delayed in notifying its customers about the breach.

Sony computer entertainment president and group chief executive Kazuo Hirai wrote that his company had notified its customers about the data theft as quickly as was possible.

Hirai said the company took time to send emails because each email contained different information. He said, "These emails are not ‘batch’ emails. The emails are individually tailored to our consumers’ accounts." He also added that Sony had blogged warning messages on its PlayStation website. (The blog was posted on 26 April.)

Meanwhile, fears that hackers may post customer data over the Internet have turned true.

Over the weekend, Sony has admitted that it had to remove customer details from an unknown website after it found that hackers had posted about 2,500 names and mailing addresses of customers.

Sony said, "The website was out-of-date and inactive when discovered as part of the continued attacks on Sony."

The company "immediately took the website down, and we are aggressively removing any residual links to the list", said Sony.