Once a Windows machine is infected, it becomes a peer in a peer-to-peer botnet controlled by a central server. If the control server is disabled by botnet hunters, the spammer simply has to control a single peer to retain control of all the bots and send instructions on the location of a new control server.
Stewart said about 20 small investment and financial news sites have been breached for the express purpose of downloading user databases with e-mail addresses matched to names and other site registration data. On the bot herder's control server, Stewart found a MySQL database dump of e-mail addresses associated with an online shop. "They're breaking into sites that are somewhat related to the stock market and stealing e-mail address from those databases. The thinking is, if they get an e-mail address for someone reading stock market and investment news, that's a perfect target for these penny stock scams," Stewart said in an interview with eWEEK.
The SpamThru spammer also controls lists of millions of e-mail addresses harvested from the hard drives of computers already in the botnet. "This gives the spammer the ability to reach individuals who have never published their e-mail address online or given it to anyone other than personal contacts," Stewart explained.
Stewart discovered that the image files in the templates are modified with every e-mail message sent, allowing the spammer to change the width and height. The image-based spam also includes random pixels at the bottom, specifically to defeat anti-spam technologies that reject mail based on a static image.The botnet is theoretically capable of sending a billion emails each day, with each having multiple recipients. And the total volume of spam has increased by 500% in the past 3 months.
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