Security

Storm botnet used to study spam

Spam is a problem that all email users suffer from but getting a handle on the economics of spamming has never been easy. A group of researchers has changed that to some extent by publishing a study [PDF] that looks at the conversion rate of spam emails. While the methods they used were somewhat ethically questionable, the data it provides is quite useful and interesting.

In the study, the Storm botnet's "command and control" (C&C) infrastructure was infiltrated in such a way that spam messages sent by Storm worker nodes would point the URLs in the spam at sites controlled by the researchers. By doing this, they could determine how much spam was sent and, more importantly, how much of it was clicked on. While sending spam is not very costly, it clearly does not have a zero cost. This means that—unbelievable though it sometimes seems—people actually do click through spam emails; not only that, they actually make purchases from the sites where they land.

The researchers set up fake pharmacy sites—selling male enhancement products amongst other things—that would be reached via the spam links. To protect the spam "victims", a visitor to the site would be allowed to get to the checkout stage before showing a site error. It seems plausible that nearly everyone willing to fill their shopping cart with such products and enter the checkout process is a very likely buyer. In this way, the study could count not only those who followed the links, but also those who were likely to buy.

What they found was that of 350 million emails sent—they estimate 82 million actually delivered—ten thousand recipients visited the site for a click-through rate of 0.003%. Of those, 28 users actually tried to check out with products totaling over $2700. The study was run for 26 days, so this could have resulted in roughly $100 per day of revenue.

Also of interest were the campaigns that were run to test the propagation of the Storm malware. This is normally done by sending spam that directs users to a website (via a "you have received a postcard" message) and entices them into clicking a link that will download and install the malware. The percentages of click-throughs were slightly higher (0.004-0.006%), but a rather large percentage of those (almost 10%) actually clicked the malware link once they reached the website. The researcher's version would download a benign executable, but the clear implication is that a small, but useful, number of users would actually add themselves to the botnet more-or-less voluntarily.

While the study is quick to point out that it represents only one data point, there is some value in extrapolating what the botnet might be able to generate in terms of revenue:

The conclusion is that something on the order of $7000-9500 per day could be generated, which equates to $2.5-3.5 million per year—a tidy sum by any measure. There is some additional speculation that because of the retail cost of sending spam (rumored to be something like $80 per million sent), it only makes sense that the Storm operators and the "pharmacies" are one and the same. The sites used for propagation of the Storm malware have similarities to those used by the shopping sites, which also indicates a close association between the two. The study makes the following, perhaps overly optimistic, argument:

The full paper is well worth a read for those interested in botnets or spam, but there are some ethical questions to consider as well. Is it reasonable to use other people's computers for your research without their consent? There is no easy answer to that question. The researchers outline their argument, which boils down to "we strictly reduce harm". Because they are just intercepting and modifying orders that are already being sent to workers, their research did not increase the amount of spam sent, nor did it increase the work that others' computers would do.

Since the spam that they arrange to be sent is harmless—at least in terms of selling bogus medicine or propagating malware—they have actually reduced the number of harmful spams sent. While their arguments seem at least well-thought-out, it is not something that would be fun to try to explain to a judge bent on enforcing some of the poorly-thought-out computer crime statutes. The researchers seem confident that their methods will pass muster, though: "We have been careful to design experiments that we believe are both consistent with current U.S. legal doctrine and are fundamentally ethical as well."

It is difficult to see how this kind of data could be gathered without co-opting Storm or another spam-sending botnet. From that standpoint, the researchers took the only path they could, but they certainly appear to have considered the legal and ethical landscape. While there may be a tendency to overestimate how widely applicable the data is—which the authors warn against—it does provide a nice look under the covers of the botnets delivering spam to one's inbox daily.

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