OSX/PrxlA is an OS X Remote Access Trojan (RAT)/Backdoor that is installed via injected legitimate applications (e.g. Img2icns, CleanMyMac, AppDelete). The applications function as expected while the malware silently installs and persists itself in the background. It was used in targeted espionage attacks in Asia and was found to be active since 2011 [1].

References:

1. http://www.thesafemac.com/new-mac-malware-discovered-icefog/