WASHINGTON, July 20 (Reuters) - Microsoft ( MSFT ) has

issued an alert about "active attacks" on server software used

by government agencies and businesses to share documents within

organizations, and it recommended security updates that

customers should apply immediately.

The FBI on Sunday said it is aware of the attacks and is

working closely with its federal and private-sector partners,

but offered no other details.

In an alert issued on Saturday, Microsoft ( MSFT ) said the

vulnerabilities apply only to SharePoint servers used within

organizations. It said that SharePoint Online in Microsoft ( MSFT ) 365,

which is in the cloud, was not hit by the attacks.

The Washington Post, which first reported the hacks, said

unidentified actors in the past few days had exploited a flaw to

launch an attack that targeted U.S. and international agencies

and businesses.

The hack is known as a "zero day" attack because it targeted

a previously unknown vulnerability, the newspaper said, quoting

experts. Tens of thousands of servers were at risk.

Microsoft ( MSFT ) did not immediately respond to a request for

comment.

In the alert, Microsoft ( MSFT ) said that a vulnerability "allows an

authorized attacker to perform spoofing over a network." It

issued recommendations to stop the attackers from exploiting it.

In a spoofing attack, an actor can manipulate financial

markets or agencies by hiding the actor's identity and appearing

to be a trusted person, organization or website.

Microsoft ( MSFT ) said on Sunday it issued a security update for

SharePoint Subscription Edition, which it said customers should

apply immediately.

It said it is working on updates to 2016 and 2019 versions

of SharePoint. If customers cannot enable recommended malware

protection, they should disconnect their servers from the

internet until a security update is available, it said.