This is the biggest since Sober in mid-to-late 2005," said Sam Masiello, the director of threat research at MX Logic, referring to a long-lasting worm whose variants struck repeatedly in the second half of 2005, often in extremely high numbers. In November 2006, for instance, e-mail filtering companies reported malware-laden e-mail counts spiking 1,500 percent in a week, and said they were intercepting four times the usual number of infected messages.