Group installs custom malware on routers to compromise firms
Microsoft still says only Outlook and Exchange Online were impacted
US State Department and the Commerce Department both affected
APT 27, APT 30, APT 31 and Gallium are said to be the perpetrators of the attacks
The company is now directing Nickel's traffic to its own servers
At least 30,000 organisations across the United States were compromised earlier this year through four security bugs in Microsoft Exchange server email software
Malaysian nationals allegedly helped Chinese hackers in their attempts to intrude into the networks of American firms
Organisations need to patch their systems immediately, they advise
The warning comes in the midst of rising tensions between the USA and China
A new variant of MgBot malware was used in latest attacks