The gang behind the attacks has compromised technology service firms and plans to use them as a proxy for attacks, security firms have said.
The group, dubbed APT10, is using custom-made malware and spear phishing to gain access to target companies.
The National Cyber Security Centre and cyber units at PwC and BAE Systems collaborated to identify the group.
"Operating alone, none of us would have joined the dots to uncover this new campaign of indirect attacks," said Richard Horne, cyber security partner at PwC.
Known victims
