Command and Control servers associated with the infamous Koobface worms have gone through a complete refresh over the last fortnight. Russian net security firm Kaspersky Lab reckons the change up might be aimed at making takedown efforts by cybercrime fighters more difficult.
Koobface spreads via messages on social networking sites such as Facebook and Twitter. The worm and compromised legitimate websites act as proxies for its main command and control servers. Infected machines are contaminated with other forms of malware, in particular scareware (rogue anti-virus), an easy and most profitable mechanism in general for cybercrooks to make money.
Over the last two weeks, researchers at Kaspersky have seen Koobface C&C servers shut down or cleaned an average of three times per day. The number of control nodes dropped steadily from 107 on 25 February, to as low as 71 on 8 March, before doubling to 142 just two days later on 10 March.
These control systems are important because they orchestrate the operation of zombie, infected drones. In the course of this process the percentage of Koobface C&C servers hosted in the US increased from 48 per cent to 52 per cent.
"The changes are a sign that botnet gangs are not just putting their malware out there but managing it like sys admins," David Emm, senior technology consultant at Kaspersky Lab UK told El Reg.
"Cybercriminals are constantly monitoring their infrastructure making sure the botnet is neither attracting too much attention nor running with too few command and control servers, which would risk them losing their control over the botnet."
Earlier this week around a quarter of the command and control servers linked to Zeus information-stealing botnet were taken offline after upstream providers pulled the plug on east European ISPs. The disruption followed a week after authorities in Spain and the US announced the arrest of three Spaniards following an early operation to take down the 12-million-plus strong Mariposa botnet.
Late last month, a court order obtained by Microsoft allowed domains associated with the Waledac spam-spewing botnet to be null routed.
Kaspersky's Emm said the Koobface gang would almost certainly be monitoring these takedown activities in devising a counterstrategy.
Kasperky Lab researchers reckon that around 100 C&C active servers, and dozens more in reserve, is the sweet-spot for the Koobface gang.
Although most of the Koobface C&C servers remain in the US, the gang has systems scattered across the world and with different ISPs, in order to make the takedown process harder.
"If the heat was increased I'm sure they could pull out of the US. The gang behind the botnet are managing and controlling their systems quite carefully," Emm told El Reg. ®