While bulk emailers have, in the past, sent unwanted messages from a single server, increasingly the spam emanates from networks of compromised PCs, known as bot nets. The level of junk email has increased almost in lock step with the number of compromised systems used for spam, said David Hart, the administrator for Total Quality Management.
“What is most alarming is that new clients – internet addresses that we have never seen before and which could be new infections – have tripled since June,” said Hart, who posted a chart (http://tqmcube.com/tide.php) tracking the growth on his Web site this week.
Bots and bot nets have rapidly emerged as one of the major threats on the Internet (http://www.securityfocus.com/brief/195).
Tens of thousands of compromised PCs are frequently counted among a single bot net’s unwilling members, with some bot nets boasting as many as a million systems (http://www.securityfocus.com/brief/19).
Traditionally, the networks have been used to install adware (http://www.securityfocus.com/news/11353) on victims’ machines or level denial-of-service attacks (http://www.securityfocus.com/news/11392) at online companies as part of an extortion scheme. Now, spammers are frequently counted among the operators or the clients of bot nets. Last May, a spammer only identified as “PharmaMaster” used a bot net to target anti-spam provider Blue Security and its Internet service providers with a massive denial-of-service attack that blocked access to the companies for hours and, in the case of Blue Security, days. Because of the attack, the company exited the anti-spam business (http://www.securityfocus.com/news/11392). Many bot herders – as the criminals that infect computers with bot software are named – sell or rent bot nets (http://www.securityfocus.com/news/11370) to others to use, and spammers increasingly seem to be among their customers.
There is strong evidence that bot nets – networks of compromised PCs – are behind the recent jump in spam. Sunbelt Software analyzed the junk email messages received by one of its dummy accounts in the past 48 hours: The 1,110 blocked messages came from 160 different mail servers as determined by their Internet addresses. The data suggests that a large number of compromised PCs are participating in sending out spma.
“It’s pretty easy, once you start breaking out the numbers, to tell a bot net from a run-of-the-mill spam server,” Greg Kras, vice president of products for Sunbelt. “Honestly, I think the increase is an attempt to keep viability by the corporations that are doing spam,” Kras said
Because many spam and antivirus filters send back a rejection message to the sender, the actual owner of the email address will be inundated with replies. Other Internet users may not notice the increase, because the spam messages are blocked by email filters or by anti-spam software on their PCs.
Security researchers that use honey pots – heavily monitored computers that are allowed to be infected by malicious software to spy on the attackers – have also confirmed the connection (http://www.securityfocus.com/brief/328) between bot nets and spam, said Thorsten Holz, a graduate student and the founder of the German Honeynet Project. “Since more and more network operators shut down open mail relays or other administrators use black lists to block these open relays, the attackers have shifted their tactics: they use compromised machines – in the form of bot nets – to send out spam,” Holz said. “We should be teaching people not to do business with criminals and to stop giving credit cards to criminals,” Hart said.
http://www.theregister.co.uk/2006/10/31/botnet_spam_surge/