Microsoft says that the malicious software programs Vobfus and Beebone, being a problem.

Two malicious software programs that help each other to get installed on computers show is difficult to remove.

The programs work together alternately downloading different variations of each other in an attempt to evade antivirus programs, Hyun Choi wrote, the Microsoft Malware Protection Center, on Sunday.

A program called Vobfus was detected in September 2009. It is known as "downloader", or program that downloads other pieces of code.

When Vobfus infects a computer, it transfers from a server command and remote control a program called Beebone, which is another type of "downloader" that installs other malware on a computer. The two work together, transferring the other variants that are not immediately detected by antivirus, Choi wrote.

"This cyclical relationship between Beebone and Vobfus to do is to download the other reason why Vobfus can seem so resilient to antivirus products," said Choi. "The updated antivirus products can detect a variation on this system, however, newer versions may not be detected immediately."

Other malware programs are known to update when a computer is infected. But if malware is detected and removed, the computer would again be infected. The approach Vobfus Beebone and makes it more likely that the computer will remain infected.

The Vobfus is also a worm that copies itself to external drives. It uses the "autorun" that is enabled on a computer, causes the Vobfus can automatically run and infect computers running Windows.

"The Vobfus has an infection rate on the removable disks very successful," Choi wrote.

(Jeremy Kirk, IDG News Service)