Microsoft on Tuesday warned that a group of hackers linked to attacks on the Democratic National Committee had exploited a vulnerability in all Windows PCs that it would not be able to fully mend for another week.

The flaw was disclosed publicly on Monday by Google, provoking a sharp rebuke from Microsoft about the dangers of revealing flaws like this before fixes are available.

Microsoft said the software flaw had been used by a group it calls Strontium, and which is known more widely as Fancy Bear. The group, which has been operating for nearly a decade, has been linked by security researchers to the Russian military and has been tied to a number of attacks on government, military and corporate systems. These include an assault on the DNC this year that is believed to have led to subsequent email leaks that have embarrassed the Democratic party in the run-up to the presidential election.