Windows workstations and servers could be hit by the ‘Downadup' worm.
F-Secure has claimed to receive several reports of corporate networks getting infected with variants of this worm since the New Year, and is working closely with affected companies as well as with various CERT organisations to fight the outbreak.
It claimed that Downadup (also known as Conficker) is a large family of network worms that is difficult to remove, especially in case of an internal infection inside a corporate network.
It can use several different methods to spread, including using the recently patched vulnerability in Windows Server Service, guessing network passwords and infecting USB sticks. As an end result, once the malware gains access to the inside of a corporate network, it can be unusually hard to eradicate fully.
Typical problems generated by the worm include locking network users out of their accounts. This happens because the worm tries to guess (or brute-force) network passwords, tripping the automatic lock-out of a user who has too many password failures.
Once this worm infects a machine, it protects itself very aggressively by setting itself to restart very early in the boot-up process of the computer, and by setting Access Rights to the files and registry keys of the worm so that the user cannot remove or change them.
The worm downloads modified versions of itself from a long list of websites. The names of these websites are generated by an algorithm based on current date and time. As there are hundreds of different domain names that could be used by the malware, it is complex for security companies to locate and shut them all down in time.
F-Secure recommends standard procedures such as checking your anti-virus vendor's website for disinfection instructions and restricting USB stick usage and block unnecessary traffic at your firewalls if you are already infected.