The attacks replace the operating system used in network equipment from Cisco, the world's biggest maker of routers, the computer forensic arm of US security research firm FireEye, Mandiant, said on Tuesday.
So far, Mandiant has found 14 instances of router implants in India, Mexico, Philippines and Ukraine, the company said in a blog post.
Separately, Cisco confirmed that it had alerted customers to these attacks on Cisco operating system software platforms.
The company said that it had worked with Mandiant to develop ways for customers detect the attack, which if found, will require them to re-image the software used to control their routers.
"If you own (seize control of) the router, you own the data of all the companies and government organisations that sit behind that router," FireEye Chief Executive Dave DeWalt said of his company's discovery.
Routers operate outside the perimeter of firewalls, anti-virus and other security tools which organisations around the world use to safeguard data traffic.
Effectively, the $80 billion (roughly Rs. 5,31,436 crores) which technology market research firm IDC estimates is spent annually on cyber-security tools offer no protection against this form of attack, according to FireEye.
The malicious programme has been dubbed "SYNful", a reference to how the implanted software can jump from router to router using their syndication functions.
Computer logs from infected routers suggest the attacks have been taking place for at least a year, FireEye's DeWalt said.
Cisco said SYNful did not take advantage of any vulnerability in its own software. Instead it stole valid network administration credentials from organisations targeted in the attacks or by gaining physical access to their routers.
The affected routers have been used to hit multiple industries and government agencies, DeWalt said.
The implanted software, which duplicates normal router functions, could also potentially affect routers from other makers, he said.
© Thomson Reuters 2015