Security maven Mary Landesman is in the midst of piecing together a who-done-it involving the infection of hundreds of websites that are generating an enormous amount of traffic. Or maybe it's a how-done-it. Either way, she's mostly drawing blanks.

Landesman is a researcher for ScanSafe, a company that monitors the web surfing of employees at large companies and provides them with real-time intelligence about what sites are spreading malware. When a client visits a site that has already attacked someone else, the service automatically blocks the site from loading in the end user's browser. Viewing some seven billion web requests per month, company researchers see a fair amount of internet gremlins.

Over the past four days, 15 per cent of the blocked malicious traffic has come from just a few hundred sites, which appear to be legitimate ecommerce destinations that have been compromised by attackers. This prompted Landesman to do some digging, and what she uncovered is unlike anything she's seen before.

For one thing, the sites themselves are hosting the malware, which is then foisted on visitors. Most of the time attackers are unable to gain such a high degree of control over the sites they hack, so they redirect end users to servers under the control of bad guys and use them to drop malicious payloads.

"I'm stumped," Landesman says. "This is a very different method of infecting the user. I want to find out how they're doing it and what is the common link between these sites."

So far, Landesman and other researchers have found no visible thread that ties the disparate group of mom-and-pop sites together. With addresses such as dubai.travel-culture.com, operationultimategoal.com and directline-citybreaks.co.uk, the sites are mostly based in the UK, but some also hail from India, Brazil and elsewhere. They don't use the same web host, and while most use web serving software from Apache, the versions vary widely, making it unlikely that attackers are exploiting a vulnerability in that program.

The outbreak coincides with another mass infection in progress that's infected tens of thousands of pages, including those of Boston University, security provider Computer Associates, and agencies from the state of Virginia and the city of Cleveland. It infects websites running Microsoft's Internet Information Server web program and the company's SQL database with links the redirect users to servers in China. The malicious sites then try to install keylogging software and other nasties.

As massive as that infection is, it's responsible for less than one per cent of the malicious traffic that ScanSafe has blocked over the past four days, a small fraction compared with the mystery sites Landesman is tracking.

The sites exhibit other intriguing characteristics. They attempt to infect visitors with a javascript file with a randomly generated name that changes each time a person visits the site. Accessing paddingtoncourt.com, for example, (we don't recommend readers try this) might result in the insertion of a script referencing a file titled xxxxx.js, which is dynamically created at paddingtoncourt.com/xxxxx.js. A different visitor might encounter a file titled yyyyy.js served from paddingtoncourt.com/yyyyy.js.

The constant flux makes it impossible for researchers to access the script responsible for delivering the payload or running Google searches that might provide a more comprehensive list of other sites that might be affected.

The script looks for various vulnerabilities specific to the visiting OS, and when it finds one pulls a .Mov file from the domain dedicated.abac.net. That in turn invokes a file from bds.invitations.fr, which installs a backdoor on end users' machines. Victims are unlikely to know they've been infected because the installation is clear and seamless, and the malware uses few PC resources. At last check, only three of 33 antivirus programs detected the malware, which appears to be a derivitive of the Rbot Trojan.

"This is pretty nasty," Landesman says. "It's a new type of compromise, and a pretty significant one." And so far very little is understood about it.

Below is a more comprehensive (though not exhaustive) list of the sites identified as infected. If you can help shed some much-needed light on these attacks, please leave a comment below or contact your reporter using this link.

hxxp://dubai.travel-culture.com/ hxxp://operationultimategoal.com/ hxxp://www.abdet.com/maps/maps-france.html hxxp://www.ace-cranes.com/ hxxp://www.aprazivel.com.br/ hxxp://www.bellingerfurniture.co.uk/ hxxp://www.bmw-carparts.co.uk/ hxxp://www.careinternational.com/ hxxp://www.directline-citybreaks.co.uk/ hxxp://www.directline-holidays.co.uk/ hxxp://www.directline-skiing.co.uk/ hxxp://www.emtbravo.com/ hxxp://www.flintoak.com/ hxxp://www.gujarat.com/recipes/ hxxp://www.henrykaye.co.uk/Cheap-bridesmaid-dresses-and-flowergirl-dresses hxxp://www.hungatecottages.co.uk/the_cottages.html hxxp://www.inthe80s.com/moviequotes/f.shtml hxxp://www.islandescapeholidays.co.uk/Dubai hxxp://www.london-discount-hotel.com/hotelinfo_id__106 hxxp://www.london-discount-theatre.com/productions hxxp://www.moorgateacoustics.co.uk/ hxxp://www.njaiche.org/main.html hxxp://www.noorcapitaluae.com/ hxxp://www.paddingtoncourt.com/ hxxp://www.panacheshoes.co.uk/ hxxp://www.peshawarjobs.com/ hxxp://www.propertyauctions.co.uk/ hxxp://www.propertyworld.com/_Bermuda hxxp://www.quaife.co.uk/Gallery hxxp://www.reallybored.net/ hxxp://www.sharpindialimited.com/dealer-locator.php hxxp://www.thirlmeremeats.com.au/family.htm hxxp://www.thirlmeremeats.com.au/special.htm hxxp://www.travel-culture.com/airblue/ hxxp://www.vauxallparts.co.uk/ hxxp://www.yournewhome.co.uk/Swan-Hill-Homes-Ltd ®