My Computer has Malware?

So, I was doing a job for a client and it involved the client giving me a flashdrive which I inserted into one of my computers (an older iMac) and I'm like 90% sure that I got Spigot (adware/malware) from it. I removed all the browser redirects/installations and then I installed Avast, but I still get this message in my Terminal "No permission to use the keyboard API for http://googleads.g.doubleclick.net". Also, my computer is starting to run slow again/makes a grinding noise sometimes. I am worried that I didn't fully remove the virus and am infected, because my computer hasn't run slow/made grinding noises since I first got the virus a couple months ago.

Help please? -Hopeful

P.S. This isn't some sort of phishing post trying to get you to go to the link I posted. I am seriously needing help here and I know this isn't a coding/virus/whatever forum, but I like BHW and thought that the audience here may be savvy to this sort of thing. Thx again

www.malwarebytes.org/ This is the software to get if you think you are having problems. The pro version has a 2 week trial which also has the chameleon mode. Some malware is pretty ferocious and will shut down and block any attempts to run software that will remove it, chameleon mode will get past that.

Good luck bro

my old pc use to grind
thats a psu issue usually the barings going on the fan
let me guess it grunts and grinds on loading then fades away

Thanks guys, but my computer that I think has adware/malware is a Mac and I couldn't use the software you recommended It does grind/grunt and slow down to freezing levels sometimes though.