Gamers and security experts had criticised Sony for its handling of the incident, which sparked lawsuits and cast a shadow over its plans to combine the strengths of its content and hardware products via online services.
The Japanese electronics and entertainment giant apologised to customers for the outage, and said a range of new security measures had been introduced. These included an early warning system that could alert the company to any attempt to penetrate the network.
"I can't thank you enough for your patience and support during this time," Sony No. 2 Kazuo Hirai said in the news release, which was also posted as a video message on the PlayStation Network blog.
"We are taking aggressive action at all levels to address the concerns that were raised by this incident, and are making consumer data protection a full-time, company wide commitment."
A single message from a PlayStation Network user under the name SG-1_F-302 on the blog read simply: "Thank you Sony!!!!"
But some users have said the prolonged outage has prompted them to switch to rival Microsoft's Xbox Live games service.
In what is thought to be the biggest security breach of its kind, hackers accessed personal information on 77 million PlayStation Network and Qriocity accounts, 90% of which are in North America and Europe, and may have stolen credit card information.
Hackers rented a server from Amazon for the attack, Bloomberg news said earlier in the day, citing a source with knowledge of the matter.
Sony discovered unusual activity on its PlayStation Network, which enables games console owners to download games, chat with friends and pit their skills against rivals, on April 19.
It shut down the network and its Qriocity online music and movie service, frustrating many users, but waited almost a week before alerting users to the extent of the security leak.
The company later found out that a separate online games service had also been penetrated, allowing access to another 25 million user accounts.
Process to be compelete by May 31
Sony said the restoration of PlayStation Network and Qriocity online movie and music services would take place on a country by country basis and that it expected the process to be complete by May 31.
Sony Online Entertainment services are also being restored and customers will be offered free game time as compensation for the outage, the company said.
Sony also said it had appointed an acting chief information officer to oversee security on its networks.
The attack on Sony is the highest-profile of a series that have affected large corporations in recent months, fuelling doubts about the security of cloud computing services.
"During the past 18 months, we've seen a dramatic rise in the volume of cyber attacks, their sophistication and their impact on businesses," Sony quoted Francis deSouza of Internet security company Symantec as saying.
Japanese games company Square Enix, known for the Final Fantasy series, said on Saturday that hackers had accessed one of its websites and obtained information, including up to 25,000 customer e-mail addresses and possibly job applicants' resumes.
The results, reported in the American Journal of Clinical Nutrition, add to evidence that sleep loss can promote weight gain -- not just by boosting hunger but also by slowing the rate at which calories are burned.
The study suggests that getting plenty of sleep might prevent weight gain, said Christian Benedict of Uppsala University in Sweden, who led the study.
"Our findings show that one night of sleep deprivation acutely reduces energy expenditure in healthy men, which suggests sleep contributes to the acute regulation of daytime energy expenditure in humans," he wrote.
Previous studies have linked sleep deprivation with weight gain and also shown how disrupted sleep also disrupts levels of stress- and hunger-related hormones during waking hours.
To help identify the exact mechanisms by which a lack of sleep might have these effects, Benedict and his colleagues put 14 male university students through a series of sleep "conditions" -- curtailed sleep, no sleep, and normal sleep -- over several days, then measured changes in how much they ate, their blood sugar, hormone levels and indicators of their metabolic rate.
They found that even a single night of missed sleep slowed metabolism the next morning, reducing energy expenditure for tasks like breathing and digestion by 5% to 20%, compared with the morning after a good night's sleep.
The young men also had higher morning levels of blood sugar, appetite-regulating hormones such as ghrelin, and stress hormones such as cortisol after sleep disruption.
Still, the sleep loss did not boost the amount of food the men consumed during the day.
A number of studies have observed that people who sleep five hours or less are more prone to weight gain and weigh-related diseases such as type-2 diabetes. But those studies do not prove that sleep loss causes weight gain.
Experts said that factors such as lifestyle and diet might add to obesity risks and that it was not clear that sleep deprivation led to obesity.
Sanford Auerbach, head of the Sleep Disorders Center at Boston Medical Center, noted that sleep deprivation is a complex issue, with medication and other issues influencing sleep as well, and urged that the new findings be kept in context.
"They showed that we adapt to sleep deprivation and that some of these adaptations could theoretically contribute to obesity," he said, adding that it's not clear how chronic sleep loss influences hormone levels.
The National Sleep Foundation recommends that adults get about seven to nine hours of sleep each night.
