WASHINGTON, Aug 20 (Reuters) - Microsoft ( MSFT ) said

on Wednesday it has scaled back some Chinese companies' access

to its early warning system for cybersecurity vulnerabilities

following speculation that Beijing was involved in a hacking

campaign against the company's widely used SharePoint servers.

The new restrictions come in the wake of last month's sweeping

hacking attempts against Microsoft SharePoint servers, at least

some of which Microsoft ( MSFT ) and others have blamed on Beijing. That

raised suspicions among several cybersecurity experts that there

was a leak in the Microsoft Active Protections Program (MAPP),

which Microsoft ( MSFT ) uses to help security vendors worldwide,

including in China, to learn about cyber threats before the

general public so they can better defend against hackers.

Beijing has denied involvement in any SharePoint hacking.

Microsoft ( MSFT ) notified members of the MAPP program of the SharePoint

vulnerabilities on June 24, July 3 and July 7, Reuters has

previously reported. Because Microsoft ( MSFT ) said it first observed

exploitation attempts on July 7, the timing led some experts to

allege that the likeliest scenario for the sudden explosion in

hacking attempts was because a rogue member of the MAPP program

misused the information.

In a statement, Microsoft ( MSFT ) said several Chinese firms

would no longer receive "proof of concept code," which mimics

the operation of genuine malicious software. Proof of concept

code can help cybersecurity professionals seeking to harden

their systems in a hurry, but it can also be repurposed by

hackers to get a jump start on the defenders.

Microsoft ( MSFT ) said it was aware that the information it provided

its partners could be exploited, "which is why we take steps -

both known and confidential - to prevent misuse. We continuously

review participants and suspend or remove them if we find they

violated their contract with us which includes a prohibition on

participating in offensive attacks."

Microsoft ( MSFT ) declined to disclose the status of its

investigation of the hacking or go into specifics about which

companies had been restricted.