Crybercrooks are beefing up the infrastructure behind the delivery of botnets, a move that is leading towards more potent and numerous threats, say researchers.

Botnet infections are commonly spread though compromised websites seeded with malicious scripts and promoted via black hat SEO tactics such as link farms. These malware networks, or malnets, pose a growing threat, according to a new study by web security firm Blue Coat.

Malnets largely deal in mass market malware and as such are different from advanced persistent threats (APTs) associated with cyber-espionage attacks targeting large corporations and Western governments. Attacks will be updated and changed, but the underlying infrastructure used to lure in users and deliver these attacks is reused. The ease with which cyber criminals can launch attacks using malnets creates a vicious cycle, a process by which individuals are lured to malware, infected, and then used to infect others.

First the malnet drives a user to the malware. Then the user’s computer is infected with a Trojan. Once the computer is compromised it can be used by the botnet to lure new users into the malnet by using the infected machine to send spam to email contact lists, for example. A compromised system can also be used to steal the victim’s personal information or money, and, in some cases, can also function as a jumping-off point for attacks on neighboring machines.

"Their [malnet] infrastructure is comprised of several thousand unique domains, servers and websites that work together to funnel users to a malware payload," Tim Van Der Horst, a senior malware researcher at Blue Coat, explained. "This infrastructure of relay and exploit servers allows malnet operators to quickly launch new attacks that can be tailored to attract large groups of potential victims."

Blue Coat expect malnets to account for more than two-thirds of all malicious cyber attacks in 2012. The firm is currently tracking more than 1,500 unique malnets, a 200 per cent (four-fold) increase from just six months ago.

The biggest malnet, dubbed Shnakule by Blue Coat, not only communicates frequently but also changes hostnames frequently, as the web filtering firm explains.

Shnakule is a wide ranging malnet that engages in a variety of malfeasant activities, including fake AV, codec, Flash and browser updates, pornography, gambling and work-at-home scams. To scale the nfrastructure to accommodate attacks associated with these activities, Shnakule operators bring new domains and servers online. Over the course of six months Shnakule used anywhere from 50 to 5,005 unique domain names per day.

Other malnets are more focused on specific malicious activities. Rubol, for example, is a spam ecosystem that operates in bursts. When it is actively launching attacks, the malnet will use as many as 476 unique domain names but this can drop to a single domain during inactive periods.

Search Engine Poisoning (SEP) continues to be the leading entry point into malnets, driving users to malware more than 35 per cent of the time. However, cyber criminals have moved away from targeting breaking news or big events. For example, of more than 28,000 successful search engine poisoning attacks in the weeks around the Olympics, only 0.18 per cent were related to the Olympics.

Email and pornography drive roughly 11 and 4 per cent, respectively, of malnet attacks. The biggest change in the last eight months had been the decline of social networking – from 6.5 per cent of all attacks to just over 1 per cent. "The full reasoning for this drop is not fully known, but part of it is attributable to greater awareness of social networking users and more robust policing of malicious content on the part of the social networks themselves," Blue Coat explains.

Looking at malware delivery infrastructures rather than infected zombies, Blue Coat has reached the conclusion that the infamous ZeuS banking Trojan toolkit is on decline.

Over the last six months a new botnet, Aleuron, has risen to take its place. Activity from the Aleuron botnet increased 517 percent, surpassing Zeus and making it the most active botnet in the wild, according to Blue Coat.

The ease with which this infrastructure can be shifted to avoid detection or target a new group of users, makes it especially tricky to eradicate malnets. ®