Security vendor Marshal is warning that web sites - predominantly in the United States and China - have been targeted in the campaign.
The security vendor warned that a variety of sensational headlines are being used to lure victims into clicking on a malicious link.
Some of the headlines include:
“Yahoo sold to Microsoft, record price;”“Some of the headlines are hard to take seriously and some of them are believably enticing,” said Phil Hay, lead threat analyst for Marshal's TRACE Team.
“Bush Down to 8 Friends on Myspace;”
"Martian Soil Fantastic for Growing Weed Says NASA;"
“Obama Is Anorexic Over-Exerciser."
“Al Qaeda Reports Declining Revenues in Fiscal '08.”
Hay said the Rustock spammers appear to be experimenting to see which types of headlines solicit the most hits from recipients.
However, if a recipient clicks on one of these links in the e-mail, a web page opens with a fake web video and a popup window that prompts the user to install a file called “codecinst.exe” so that the video will play properly. Doing so downloads malware that installs the botnet software.
“They are trying to disguise the installation of the executable under a believable pretext,” said Hay.
Marshal's records revealed that the Rustock botnet included more than 150,000 infected PCs and distributes close to 30 billion spam messages daily, which in terms of volume makes it one of the biggest malicious spam campaigns ever seen.
“Rustock is not a name many people are familiar with but it is well known within the security industry. Today it is one of the most established spambots. Rustock has been operating in various forms for more than two years,” said Hay.
At one point, it was responsible for 21 percent of the spam clogging inboxes, according to Marshall in a report earlier this year.