Vobfus has been around the block a few times, some Visual Basic code that first popped up in 2009 which tried to download and install code to attack machines that managed to get Vobfus on their systems.  Beebone, aka Win32/Beebone is newer, a fairly common Trojan infection which is similar to Vobfus in that it attempts to download other malware as opposed to attacking your machine directly.  According to this story on The Inquirer, they have developed a symbiotic relationship, where when one infects you it immediately tries to infect you with the other.  That way it can fool anti-malware programs into beleiving that they've sanitized your machine of all infections when in fact you only remove one of the two infections and the remaining one immediately downloads and installs a different variant of the one you just removed.

"SOFTWARE HOUSE Microsoft's security researchers have discovered a pair of malware programs that help one another to avoid being detected by antivirus software.

Known as Vobfus and Beebone, the collaborating malware prove difficult to remove from infected machines as they work together, foiling the removal by regularly downloading updated versions of their respective partners."

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