Here's a quote from a blog we wrote awhile back when we first announced Mariposa. It should help with understanding the botnet name versus the malware involved:
"Our naming of this botnet as Mariposa has been a cause of concern for some. The confusion comes when antivirus companies or those using antivirus, search for the Mariposa name only to find no results. This is because Mariposa refers to the botnet and not the malware it utilizes."