How Does So Much Spam Come From One Place?

Brian Krebs Staff Writer
Tuesday, November 18, 2008 9:00 AM

At roughly 4:30 p.m. Eastern time last Tuesday, the volume of junk e-mail arriving at inboxes around the world suddenly plummeted by at least 65 percent, an unprecedented drop caused by what is believed to be a single, simple act.

According to security experts, one Silicon Valley based computer firm was playing host to computers of various organizations that controlled the distribution of much of the world's spam. Confronted with evidence tracing the spam activity back to the hosting firm, McColo Corp., Internet service providers pulled the plug, severing McColo's online connections.

By nearly all accounts, spam volumes have remained at far diminished levels, though experts interviewed for this story expect spam to soon bounce back or even exceed previous levels. But the question remains: How could such a massive concentration of spam activity be hosted for so long from the servers at a single U.S.-based facility, in the belly of the security and tech community in Silicon Valley?

The answer exemplifies how complex the battle against spam has become. Like other Internet hosting firms, McColo -- which has not been charged with any crime and has been unavailable for comment -- assigns certain Internet addresses for its clients' computers to use. In effect, that's how those firms operate on the Web.

But the spam often does not come directly from those computers, according to security experts who have documented the activity. Rather, McColo appears to have been home to a number of key Internet servers -- computers that control networks of computers -- that were used by their respective owners to coordinate the actions of hundreds of thousands of PCs that may be compromised with malicious software designed to turn them into spam-spewing zombies.

According to research by several in the computer security community some of the largest collections of hacked PCs, known as robot networks or "botnets," may have had their master control servers hosted at McColo. Assigned such curious monikers such as "Srizbi," "Rustock," "Mega-D" and "Cutwail" by anti-virus vendors, the networks of compromised computers around the world are named after the malicious software that powers them.

The botnets typically are rented out to junk e-mail purveyors. The spammers then sign in remotely to those control servers and use them to coordinate the sending of billions of e-mails a day touting everything from knockoff pharmaceuticals and designer goods to pornography and get-rich-quick scams.

But when McColo was taken offline by its Internet providers, so, too, were all of the botnet control servers located there. That means hundreds of thousands of computers that remain infected with these bot programs were left like sheep without a shepherd, waiting and searching the Web for a new set of instructions from the criminal gangs that controlled them.

Joe Stewart, director of malware research for Atlanta-based SecureWorks, said some botnets might remain disconnected. For the moment, the Internet's three largest spam botnets appear to be stranded and unable to contact more than a small number of their control servers, according to Marshal, a computer security firm in the United Kingdom that tracks bot activity.

Both Stewart and Marshal say the criminals responsible for maintaining those botnets will quickly find ways to revive them.

Not everyone has seen fewer spam messages in their inboxes after McColo's shutdown. Adam O'Donnell, director of emerging technologies at Cloudmark, an e-mail security company in San Francisco, said those who did not see a drop in spam from the McColo shutdown likely subscribe to an Internet service provider that already does an effective job blocking 99 percent of junk e-mail.

"People who had really good systems in place probably didn't benefit from this, while those who had more marginal spam filter protection likely saw a significant drop off in spam," O'Donnell said.

Evidence collected by anti-spam groups strongly suggests that not only was McColo hosting major gateways for the sending of spam, but it also was home to the most world's most aggressive e-mail address harvesting services.

In the underground spam economy, e-mail addresses are a valuable commodity, as they represent both the beginning and end points of any junk e-mail operation. Spam distribution lists typically are assembled using automated computer programs, or "bots," that continuously trawl millions of Web sites much the way that search engines do -- scouring them for e-mail addresses.

The addresses are then sold to spam networks, which use them as not only the destination for their junk e-mail, but also as the apparent source -- by "spoofing" the messages to make them appear as though they were sent by real, live e-mail users.

In many cases, those responsible for harvesting e-mail addresses are not the same people sending the spam, but rather individuals who will sell the lists to known spam operators.

Matthew Prince, chief executive of Unspam Technologies and founder of Project Honey Pot, a collaborative effort that secretly gathers intelligence about the world's largest spam networks, has tracked the spam harvesting bots hosted at McColo for more than two years.

Project Honey Pot's free technology, which is deployed at more than 20,000 Web sites, tries to track these crawler bots by assigning a unique "spam trap" e-mail address to each participating site. The dummy addresses are designed to be difficult for humans to find but very easy for the bots to gather. The project's software then records the Internet address of any visitor and the date and time of the visit. Because those addresses are never used to sign up for e-mail lists, the software can help investigators draw connections between harvesters and spammers if an address generated by a spam trap or "honey pot" later receives junk e-mail.

Prince said statistics from Project Honey Pot suggest that crawler bots hosted at McColo are responsible for more than 30 million spam messages sent to the project's e-mail traps since June 2006.

"And our spam traps constitute a tiny fraction of the e-mail addresses in the world," Prince said.

The project estimates that each e-mail address harvested by bots at McColo could expect to receive an additional 2,000 junk e-mail messages a year as a result. Such activity could have major implications for businesses that list large numbers of employee e-mail addresses on their Web sites.

"Consider what this activity means for, say, a single law firm that publishes on its site the e-mail addresses for each of its 50 attorneys," Prince said. "After the firm's site gets crawled by the bots at McColo, that means that firm can expect to receive at least 100,000 more pieces of spam than it would have otherwise."

While there are hundreds of millions of e-mail addresses already registered, spammers need every address they can get their hands on because such a tiny percentage of people who receive the messages actually buy anything from them.

A study by University of California researchers released in October estimated that the criminals behind the Storm worm -- which powered a botnet once responsible for sending about 20 percent of all spam -- made on average between $7,000 and $9,000 a day sending pharmaceutical spam. But the Storm worm purveyors had to send prodigious amounts of spam to gin up a single customer: The researchers found that while only about 1 in every 12 million spam e-mails turned into a sale, that was enough to keep the spammers in business.

Despite the level of questionable activity researchers say was coming out of networks hosted at McColo, it's not clear what if anything federal law enforcement can or should do about it, or whether anyone at the company has committed any crime.

A spokesman for the FBI declined to comment for this story, as did the U.S. Secret Service. A federal law enforcement official familiar with the accusations against McColo said privately that authorities have been investigating the hosting provider, but that building a case that could convince a jury of McColo's complicity in the activity has proven difficult.

Some in the security community, while applauding McColo's Internet providers for cutting the company off, said it should have happened sooner.

John Bambenek, incident handler with the SANS Internet Storm Center, which tracks hacking trends, said he doubts either provider was unaware of the alleged activity at McColo.

"The upstream providers may claim they didn't know, but that's about as convincing as a motel operator who is renting rooms by the hour and hearing the exploits from the hallway and being shocked when the police show up to bust the prostitution ring," Bambenek said.

But Benny Ng, director of infrastructure for Hurricane Electric, one of the Internet providers that cut off McColo's online connections, said that "until we were provided with the Washington Post report, there was no compelling overall picture." He added that many people, "including some professionals, think it is perfectly reasonable for an Internet service provider to intercept and inspect their customers traffic, including reading customers' email. Hurricane Electric does NOT condone or practice this, as this is illegal due to privacy laws."

Ng said his company monitors spam blacklists for Internet addresses used to send spam, but even those lists would not have flagged the botnet control servers hosted by McColo.

"Specifically in this case, the scope and complexity [of what was going on at McColo] was nearly imperceptible," said Ng. "The indirect nature of this network abuse, with compromised computers all over the world, was particularly subversive."

Global Crossing, the other major provider that pulled the plug on McColo's access, refused to comment.

If U.S. law enforcement was reluctant to act against McColo before the company's Internet providers pulled the plug, there are no signs that they any more willing after the incident. Sometime on Saturday, McColo's principals briefly reconnected the company's Web servers to a major Internet provider in Europe.

"The best part about this story is that they haven't physically moved their servers... they're still in Market Post Tower in sunny San Jose," at the very same Internet addresses, wrote Atif Mushtaq, a researcher and engineer at Fireeye.

Fireeye said the European ISP on Sunday severed its relationship with McColo under pressure from the security community. But that may have been enough time for criminals behind the Rustock botnet to reclaim control of between 10,000 and 15,000 of the estimated 100,000 computers infected with the malware, Fireeye estimates.

Experts say it's not uncommon for cyber criminals to stage their operations out of the United States, regardless of where the criminals themselves may be based. After all, U.S. Internet providers offer some of the fastest, cheapest and most reliable Internet services on the planet.

"These guys like going after well-hosted infrastructure in good economies, because it gives them the resiliency that any business looks for," said Vincent Weafer, senior director of development for Symantec Security Response.

What's more, dependability and server uptime are important in cutthroat businesses for which an outage of a few hours can staunch the flow of spam and cost thousands of dollars.

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