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Latvian ISP closure dents Cutwail botnet

Level 2
Real Host, an ISP based in Riga, Latvia was alleged to be linked to command-and-control servers for infected botnet computers, as well as being linked to malicious websites, phishing websites and “rogue” anti-virus products.  Real Host was disconnected by its upstream providers on 1 August 2009. The impact was immediately felt, as can be seen in Figure 1, where spam volumes dropped briefly by as much as 38% in the subsequent 48-hour period. 

Much of this spam was linked to the Cutwail botnet, currently one of the largest botnets and responsible for approximately 15-20% of all spam. Its activity levels fell by as much as 90% when Real Host was taken offline, but quickly recovered in a matter of days.

Figure 1 shows the relative proportion of spam originating from the five major botnets globally during the period of this attack: Cutwail, Xarvester, Rustock, Mega-D, and Donbot. The scale used is a relative index based on the relative volumes and spam rate originating from each botnet. It is not an indication of the size of the botnet or the volume of spam directly. In the next report, MessageLabs Intelligence will be taking a closer look at some of these major botnets.

Figure 1 - Relative proportion of spam from top-5 most active botnets when Real Hosts was taken offline

This was not the first time an ISP blamed for malicious activity has been disconnected. In the last 12-months at least three US-based ISPs have suffered a similar fate, most notably, Atrivo (aka InterCage), McColo and Pricewert (3FN). Pricewert was taken offline by the US Federal Trade Commission.

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