Sometimes deleting old system restore points can help. What anti virus do you use? Does it pick up the virus and if you delete it does it still come back? If so, then the system restore points have been infected too. Disable system restore and reboot and the virus usually goes.
Bear in mind i've never been infected by zwangi malware so I haven't had this experience before. I am only giving my advice on previous problems with other backdoor Trojans.
First you need a virus programme that recognises zwangi and tries to delete it. If it then still exists in the system it normally has infected system restore points and this is why it comes back. Turn off system restore which deletes old points and then reboot the computer.
Sometimes this works.
If the system is then cleaned don't forget to enable system restore again.
There are some programmes that say they can deal with this problem, but usually they charge you for the service.
Sometimes I feel they put the viruses out themselves knowing they have the tool to get rid of. An utter scam!!!