HandBrake team, writing on their forum: Anyone who has downloaded HandBrake on Mac between [02/May/2017 14:30 UTC] and [06/May/2017 11:00 UTC] needs to verify the SHA1 / 256 sum of the file before running it. Anyone who has installed HandBrake for Mac needs to verify their system is not infected with a Trojan. You have 50/50 chance if you've downloaded HandBrake during this period. If you see a process called "Activity_agent" in the OSX Activity Monitor application. You are infected. HandBrake is a popular, open-source video conversion tool. The team hasn't issued any advisory for Windows users.