The hackers who breached Google's network last year were able to nab the source code for the company's global password system, according to The New York Times.

The single sign-on password system, which Google referred to internally as "Gaia," allows users to log into a constellation of services the company offers – Gmail, search, business applications and others – using one password.

The hackers, who are still unknown, were able to steal the code after gaining access to the company's software repository, which stores the crown jewels for its search engine and other programs.

Because the hackers grabbed the software, and do not appear to have grabbed customer passwords, users aren't directly affected by the theft. But the hackers could study the software for security vulnerabilities to devise ways to breach the system that could later affect users.

Google announced in January that it and numerous other companies had been hacked in a sophisticated attack. The hackers had targeted source code repositories at many of the companies, including Google.

According to the Times, the theft began when an instant message was sent to a Google employee in China who was using Windows Messenger. The message included a link to a malicious website. Once the employee clicked on the link, the intruders were able to gain access to the employee's computer and from there to computers used by software developers at Google’s headquarters in California.

The intruders seemed to know the names of the Gaia software developers, according to the Times. The intruders had access to an internal Google corporate directory known as Moma, which lists the work activities of every Google employee.

They initially tried to access the programmer's work computers and "then used a set of sophisticated techniques to gain access to the repositories where the source code for the program was stored."

The Times doesn't elaborate on the set of sophisticated techniques the hackers used to access the source code, but in March, security firm McAfee released a white paper in relation to the Google hack that describes serious security vulnerabilities it found in software configuration management systems (SCMs) used by companies that were targeted in the hacks.

"[The SCMs] were wide open," Dmitri Alperovitch, McAfee's vice president for threat research told Threat Level at the time. "No one ever thought about securing them, yet these were the crown jewels of most of these companies in many ways — much more valuable than any financial or personally identifiable data that they may have and spend so much time and effort protecting."

Many of the companies that were attacked used the same source-code management system made by Perforce, a California-based company, according to McAfee. The paper didn't indicate, however, whether Google used Perforce or had another system in place with vulnerabilities.

According to McAfee's earlier report, the malicious website the hackers used in the Google hack was hosted in Taiwan. Once the victim clicked on a link to the site, the site downloaded and executed a malicious JavaScript, with a zero-day exploit that attacked a vulnerability in the user's Internet Explorer browser.

A binary disguised as a JPEG file then downloaded to the user's system and opened a backdoor onto the computer and set up a connection to the attackers' command-and-control servers, also hosted in Taiwan.

From that initial access point, the attackers obtained access to the source-code management system or burrowed deeper into the corporate network to gain a persistent hold.

According to the paper, the hackers were successful at accessing source code because many SCMs are not secured out of the box and do not maintain sufficient logs to help forensic investigators examining an attack.

"Additionally, due to the open nature of most SCM systems today, much of the source code it is built to protect can be copied and managed on the endpoint developer system," the white paper states. "It is quite common to have developers copy source code files to their local systems, edit them locally, and then check them back into the source code tree.... As a result, attackers often don't even need to target and hack the backend SCM systems; they can simply target the individual developer systems to harvest large amounts of source code rather quickly."

Alperovitch told Threat Level his company had seen no evidence to indicate that source code at any of the hacked companies had been altered.