Microsoft says a newly discovered flaw in its Windows software was used by a hacking group that other researchers have linked to Russia’s government and computer intrusions at the Democratic National Committee.

The flaw was detected by researchers at Google, who recently alerted software makers Microsoft and Adobe Systems about vulnerabilities in their programs. Adobe issued a fix for its software last week. Microsoft says it’s testing a patch and will release it next week.

Microsoft acknowledged the problem Tuesday, saying only that it affected older versions of Windows and was used by a group called Strontium to target “a specific set of customers.”

The security firm Crowdstrike and others have linked Strontium, also known as “Fancy Bear,” to recent attacks on government, media and political targets in several countries.

According to Reuters, Adobe issued a patch on the vulnerability on Monday after Google researchers disclosed the flaw.

Microsoft also criticized Google for reporting the flaw.

“Google’s decision to disclose these vulnerabilities before patches are broadly available and tested is disappointing, and puts customers at increased risk,” Microsoft said.