Spokeswoman Jen Psaki said companies should take it very seriously.

This is an active threat, and as the national security adviser tweeted last night, everyone running these servers government, private sector academia needs to act now to patch them.

CNN separately reported on Sunday that US President Joe Biden was forming a task force to address the hack.

A source told Reuters it's now believed more than 20,000 U.

S organizations had been affected, including e credit unions, town governments and small businesses.

Major companies in federal agencies appear to have been spared, according to initial findings.

Microsoft has pointed the finger at hackers from China, but Beijing denies its involvement.

The tech company released a patch last week to address flaws and outlook.

It's email software, but the remedy can only defend against new hacking attempts.

The White House National Security Council tweeted on Sunday.

Patching and mitigation is not remediation.

It is essential that any organization with a vulnerable server take measures to determine if they were already targeted.

Neither the company nor the white House has specified the scale of the hack.

Microsoft initially said it was limited, but the White House last week expressed concern about the potential for a large number of victims.

A Microsoft representatives said it was working with the government to guide vulnerable clients as more attacks are expected.