The viruses were found on office computers and in a system used to model the movement of nuclear fuel rods. By chance, the viruses caused no threat to the Gundremmingen nuclear plant because its control systems were not linked to the internet, in effect the viruses could not set off.  

How the plant got infected German is now under federal cyber investigators' analysis. The viruses were found on 18 USB sticks used as portable drive storage for office computers and on the fuel rod modeling structure. The nuke plant is ran by the German utility RWE.

Plant Staff found the viruses while preparing to upgrade the computerized control systems for the plant's Block B that is presently not generating power while it experiences scheduled maintenance.

About a thousand more computers have been already checked for infectivity and cleaned up, newspaper Die Zeit reported. Security has already tightened up due to the virus alarm.

There are no system directly caught up with the control of the nuke reactors was infected and danger to the public is far behind result of the infection. All sensitive plant areas are controlled and protected against exploitation, RWE said.

The viruses were the well-known malicious programs, W32.Ramnit and Conficker. Also found in the USB sticks are Malware. Ramnit dates from 2010 and is a remote access tool that its founders use to take data from private servers while Conficker debuted in 2008 aiming to steal log-in usernames and financial information.

Since the infected do not have access to the net, both Ramnit and Conficker were not able to activate, update and grab data, RWE added.

F-Secure Chief Research Officer Mikko Hypponen said that power plants and other branch of a nation's important infrastructures were often infected by viruses but these attacks did modest harm, Reuters reported.

The Gundremmingen nuclear power plant, about 120km (75m) northwest of Munich, is Germany's highest productivity power station.