The latest March 8th release of Malicious Software Removal Tool (MSRT) included detection and cleaning capabilities for a backdoor enabled worm called "Win32/Renocide".
"According to MS telemetry, this new addition was among the top 5 detected threats (in the first week of release), both when when classified based on number of detected files and number of infected machines. The high tally of affected machines reflects Renocide's relative age; the botnet has been around since 2008 and has slowly but steadily increased its prevalence.
If you look at the ranking for machine count you'll notice that the first 2 families are also worms. Rimecud is a backdoor-enabled worm (just like Renocide), while Taterf is an account stealer. Although only third when it comes to machine count ranking, Sality leads in the threat count ranking due to the fact that it is a file infector," stated Microsoft's MMPC blog.
If you are not familiar with this threat, you can read more about all malware families present in the encyclopedia.>[Source]