Rootkit named as "Necurs" infect 83,427 unique machines during the month of November 2012. It is a multi-purpose rootkits capable of posing a threat to both 32 and 64-bit Windows systems. Distributed via drive-by download on the websites that host the BlackHole exploit kit.
Like other rootkits it is able to hide itself from detection and also capable of downloading additional malware from outside. Attackers can maintain remote access to a machine this way in order to monitor activity, send spam or install scareware.
Rootkit also stop security applications from functioning and hence no detection. Microsoft list this as Trojan:Win32/Necurs.
Trojan:Win32/Necurs is a family of malware that work together to download additional malware and enable backdoor access and control of your computer. The malware can be installed on its own or alongside rogue security software, such as Rogue:Win32/Winwebsec.