DarkComet is one of a handful of commercially available RATs, many of which are advertised as benign tools for use by administrators to control remote machines. But many of the tools of course are used by attackers to compromise and control victims machines as part of targeted attacks or other campaigns. The Syrian government used the tool to keep tabs on citizens who were anti-government activists. The author said that the use of his RAT for malicious purposes by hacking groups was a major factor in his decision to kill the tool.
Source: https://threatpost.com/darkcomet-rat-flames-out-070912/76777/