'Significant' vulnerabilities in Microsoft's Exchange servers -WH
White House press secretary Jen Psaki said the vulnerability posed "an active threat" that could have far-reaching consequences.
"We're concerned that there are a large number of victims," she said.
More than 20,000 American organizations have been compromised through a back door installed via a recently patched flaw in Microsoft Corp's flagship email software program, a person familiar with the U.S. government's response to the hacking spree said on Friday.
