A computer worm is a type of malware that attempts to spread itself to other computers over the internet or local networks. Stuxnet was designed to attack Windows systems running Siemen’s Plan 7 software. The worm itself was transmitted to the computers of employees of 5 companies which were connected to the Natanz facility. The worm would then copy itself to flash drives and disks that were connected to those computers. When those drives were connected to computers within the Natanz facility, they would spread the worm to all the computers connected to the network. Only computers running the Plan 7 software would be significantly affected by the software. This was to decrease the likelihood of detection. Once the worm had made it onto the target computers, it would begin modifying the variables that the centrifuges required, such as spin speed and time.