Rumor, innuendo, etc. is that his software was spyware back in the day.
An example; one rumor was that he donated laptops with his software to government agencies, although he wasn't 'fond' of government agencies. Stuff like that.
Gist of many is that McAfee had some kind of grudge against the Clintons, mostlly Hillary, IIRC.
So, in a nutshell; A guy with fuck you money and a grudge. You can follow the dots as to what he might have.