Gumblar is a multi-stage attack that infects compromised machines with a number of separate pieces of malware. It also has the ability to steal credentials and block the victim from taking actions to clean his PC. The attack, for all its sophistication, still relies on the basic drive-by download technique to infect machines. Some estimates have Gumbler responsible for more than 40% of all Web site infections. The only good news appears to be that the Chinese domains controlling the infections are down for the time being.
Source: https://threatpost.com/gumblar-malware-sweeping-nation-052209/72757/