99.99% of malware is completely hidden from sight. Malware authors aren't interested in having their exploits detected by suspicious users. While malware can't be entirely ruled out in your case, you are probably experiencing some kind of software or hardware problem (maybe the GPU.)
My best advice is that you probably shouldn't be installing any antivirus or spyware detection software on your Mac. Please hear me out and let me explain why: I know that every few months some tech journalist gets the juicy idea to (again) run. The Best Free Anti-Spyware app downloads for Mac: Malwarebytes Anti-Malware Little Snitch MacScan Boonana Trojan Horse Removal Tool DNSChanger Removal. Best Video Software for the Mac How To. The Mac isn't immune to viruses, Trojans, backdoors, adware, spyware, ransomware, and other nefarious applications. The main difference between Macs and Windows is that no successful viruses written for OS X have shown up in the wild, that is, outside of a security research organization. Here is the list of some of the best anti-malware software for Mac to prevent your Mac from being victimized further and for malware removal from Mac. As malware, spyware, adware, ransomware and all other viruses could be really dangerous for your Mac and the system files. Top 10 Best Free Spyware Removal Software 2018 Get full antivirus protection and remove all spyware today! Spyware is malicious software which finds its way onto your computer and will track data about you and your computer usage and use this to obtain sensitive information about users or intercept advertising on your computer.
Using a constantly on AV program runs the risk of slowing down your Mac, or creating other issues. In addition, no AV program can identify an infection that hasn't yet been catalogued, and most AV programs use heuristics--in plain talk they are making educated guesses, which often lead to false positives. You may still want to run some kind of AV. The best bet out there is probably Sophos, or VirusBarrier Express (scans only manually and makes no system modifications. MacKeeper is total garbage. Although it does now use a respectable AV program, Avira, you could run that without buying the whole package.
ClamXav is a decent program run by a developer with considerable integrity, but it has fallen way behind in its detection rate. And MacScan is pathetic at identifying malware. But is the best at finding known keyloggers. And as far as I know, most if not all of those will have needed to be installed with physical access to the Mac.
Best Antivirus Spyware For Mac
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Here's a good read on this subject.