It is the first time that such a defense plan has been noticed before. Choi said that the Vobfus and Beebone viruses, were regularly found together. Vobfus was the first to arrive on a machine, he said, and used different tactics to infect victims. Vobfus could be installed via booby-trapped links on websites, travel via network links to other machines or lurk on USB drives and infect machines they are plugged into.
Once installed, Vobfus downloaded Beebone which enrolled the machine into a botnet. After this the two start to work together to regularly download new versions of each other. If Vobfus was detected and remediated, it could have downloaded an undetected Beebone which can in turn download an undetected variant of Vobfus.
Vobfus become a persistent problem since 2009 when it first appeared.