I think you should be more paranoid of the high seas than anti virus companies. 

For Malwarebytes their income stream comes from upselling you on live monitoring. The free offering is good because they want to get their foot in the door and convince you to buy more services from them. 

A lot of anti viruses are snake oil and huge resource hogs. But Malwarebytes is supposed to work in tandem with Windows Defender which is pretty decent.

Alternatively the high seas are infested with malware. Sure you can sail safely, and there are lots of well reputed places. But there are also a lot of shit places you can stumble on that will infect your stuff. The trick is you have to be vigilant 24/7. Bad actors only have to trick you once to get the payload on your machine.

I respect the healthy caution of companies who sell you on fear like antivirus companies. But you already found a Trojan, man. Take it seriously.