On Saturday, Kazuo Hirai, who heads Sony's consumer products and services group, said in  a video blog that while services are still being restored in phases, most users around the world will now have access to PSN, Qriocity, online multiplayer games, and third-party services such as Netflix and Hulu. The full restoration is scheduled to be completed by the end of the month.Hirai said that PSN and other services have remained offline while Sony bolstered their security features. "Our upgraded system includes components such as advanced security technology, increased levels of encryption, additional firewalls, and a new early warning detection system for any unusual activity that could signal an attack on the network," he said.Security-wise, Sony also released new firmware (version 3.61) which will be mandatory for using a PlayStation 3 (PS3) to go online. The firmware also requires all PS3 users to change their passwords before they can use the machine to go online. The password can only be changed from a user's own PS3, or from the PS3 on which a PSN account was first activated. First-time users can create a password by using their registered email address.But on Sunday, Sony was having difficulty keeping up with the large number of resulting password-reset requests. Patrick Seybold, Sony's senior director of corporate communications and social media, said in a blog post that "we're currently experiencing an extremely heavy load of password resets, and so we recently had to turn off services for approximately 30 minutes to clear the queue." Going forward, he said that password reset requests might not be immediately fulfilled.Sony is also offering free identity theft insurance in countries where such programs exist. But it's unknown whether the company will release police reports related to the intrusions. That would allow affected consumers in the United States to create a free credit freeze to further protect against identity theft.As PS3 users regain access to online Sony services, another question remains: How was Sony breached? To date the company hasn't provided a full explanation of how attackers broke into its systems.On Friday, Chris Lytle, a security researcher at Veracode, said in a blog post that Sony's fullest explanation of the attacks--in a letter to Congress--"seems like a roundabout way of saying that there was a SQL injection issue in one of PSN's applications or that the database server could have been publicly accessible and exploitable from there." Of course, that still doesn't include much detail.But Lytle says that based on what's known, it's likely that Sony's site was compromised using one of four techniques: physically attacking a Sony server; via an insider attack possibly related to Sony laying off 205 SOE employees on March 31; using a PS3 with developer credentials to hack into PSN; or via an unpatched server.In terms of using a PS3 against PSN, "in one attack modders found it was possible to force a PS3 to connect to the [production/quality assurance] instance of PSN," said Lytle. "On this particular instance, the servers would not authenticate credit card information before adding credit to the account, so attackers could simply add unlimited credit for the PSN store. Much of this information was publicly available before the breach happened."But hacking Sony via an unpatched server seems the most likely explanation. For starters, it's bolstered by a supposed pre-attack chat log that says PSN was using unpatched versions of Apache and Linux. "It is a solid bet that if those packages were outdated, the rest of the server hadn't been patched in the last five years either," said Lytle. On the other hand, "Google's Web cache shows that Sony's servers were up to date, so this whole theory may be bunk."But Bloomberg on Friday quoted an unnamed source who said that "hackers using an alias signed up to rent a server through Amazon's EC2 service and launched the attack from there." If that's true, it strongly suggests that attackers found unpatched server software on the Sony site and used known vulnerabilities to gain entry to Sony's systems.In the new, all-digital issue of InformationWeek: Our 2011 Strategic Security Survey shows increased executive interest in security. Here's what you should do next. Download it now. (Free registration required.) 