The US nuclear weapons agency is among the victims of an alleged Chinese hack. Microsoft

A cyberattack on Microsoft's SharePoint document management software has affected the agency responsible for maintaining and designing the United States' nuclear arsenal.

According to Bloomberg, there is no evidence that the hack compromised any sensitive or classified information, but various parts of the department were reportedly affected.

Hackers exploited flaws in the widely used SharePoint document management software, in some cases stealing login credentials, including usernames, passwords, hash codes, and tokens. The hack affected around 100 organizations.

The extent of the damage is unknown. Hackers have broken into national government systems in Europe and the Middle East and other U.S. departments.

The US media outlet reported that the attack affected systems belonging to national governments in Europe and the Middle East, the US Department of Education, the Florida Department of Revenue, and the Rhode Island General Assembly.

Although the perpetrators of the attack are still unknown, Microsoft and Google have attributed the attack to Chinese state-sponsored hackers. They are believed to be two groups of hackers, allegedly Chinese, dubbed "Linen Typhoon" and "Violet Typhoon," who allegedly exploited the vulnerabilities, along with a third, also based in China. The Chinese embassy in Washington has condemned the attack and denied responsibility, accusing them of "defaming others without solid evidence."

Microsoft knew about the security flaw, but did not patch it effectively.

A Microsoft spokesperson confirmed that the company learned of this security flaw during a hacking competition in May, and that the security patch that was released did not fully address the critical flaw in the SharePoint server software.

The cyberattack affected approximately 100 organizations over the weekend, and is expected to spread as other hackers join in. The full extent of the damage is currently unknown.