Constantly getting Backdoor.optix

I am constantly getting backdoor.optix showing up in scans, every 2 weeks or so. I also notice https pages always show error msgs when this occurs, as well as youtube video only loading for a fraction of the specified time, winrar files also become corrupted, even though the archive is perfectly fine, and others that have extracted the archives with no problems, email me their files, but I still get "unexpected end of file" "file is corrupt" msgs.

Here is my hijackthis log:

 

Hi estado,
Welcome to Major Geeks!

Please go through the instructions in the READ & RUN ME FIRST and attach the requested logs with your next post. If you still have a copy of your HJT log, please attach it before you get started with the rest. What scans have you done that are picking up Backdoor.optix?

abri