OSX/IServiceA is an OS X Backdoor that was spread via a trojaned iWork '09 free trial installer shared on peer-to-peer networks [1]. Discovered in early 2009, OSX/IServiceA was one of the first two signatures introduced into XProtect, when silently released as a part of Mac OS X 10.6.0 Snow Leopard [2].

References:

1. https://www.symantec.com/connect/blogs/osxiservice-it-s-not-going-iwork-you
2. http://www.macworld.com/article/1142457/snowleopard_malware.html