A growing number of illegal online pharmacies are flooding the web trying to sell dangerous unauthorized prescriptions, according to a new report from cybersecurity experts at Carnegie Mellon University.

Report authors Nicolas Christin, associate director of the Information Networking Institute (INI) and a senior systems scientist at the INI and CyLab along with Nektarios Leontiadis from the Department of Engineering and Public Policy (EPP), and Tyler Moore from Wellesley College, found that rogue websites were redirecting consumers to illicit pharmacies.

By researching the top search results for 218 drug-related queries over nine months in 2010 and 2011, Christin's research team found evidence of substantial manipulation of web search results to promote unauthorized pharmacies.

"We have known for some time that unauthorized online pharmacies have been using email spam to tap the wallets of unwary online consumers, but that method did not blanket enough customers so now the online thieves are infecting websites to redirect unwary consumers to hundreds of illegal online pharmacies,'' Christin says.

Christin reports that his team found that one-third of the collected search results were of 7,000 infected websites triggered to redirect to a few hundred pharmacy websites. One quarter of the top 10 search results were observed to actively redirect to illicit pharmacies, and another 15 percent of the top results were for sites that no longer redirected, but had previously been compromised.

Using estimates of the popularity of drug-related search terms and the payment-processing websites used by pharmacies, Carnegie Mellon researchers report that search-engine manipulation is considerably more efficient than email spam.

"So, to those who aim to reduce unauthorized pharmaceutical sales, more emphasis needs to be made in combating transactions facilitated by web search,'' said Christin.