Various threats found to system

[ArtVandelay]

Longtime malwarebytes user.  Recently became concerned about the threat of potential threats to system after I noticed some lagginess. I downloaded Avast to be safe and to "provide another set of eyes".    The scan found several infections that weren't found by malwarebytes and I was hoping of asking one of the trained experts here if any of these files pose a threat to my mac. 

I'd be appreciative of any help and information you can provide.  I really trust you guys and am appreciative of all the good work you do. 

Thank you in advance. 

[treed]

None of those are actually threats to your Mac. They're all just files from your Safari cache, and quarantining them does absolutely nothing to make you more secure.

One thing that I notice is that some cryptocurrency miner scripts were found in your Safari cache, which means that you have visited one or more sites that is using your computer's CPU to mine cryptocurrency. This could very well explain your performance issues. Keep an eye on Activity Monitor when you see performance problems, and if you notice that a particular website is using a most of the CPU time, that's the site that is the culprit. You'll want to avoid that site in the future.

[ArtVandelay]

Thank you very much for your quick response on this and for giving me the peace of mind.  

Just to be clear, so I am armed with the knowledge for the future: 1) certain websites use my CPU's power to mine cryptocurrency without giving them any permissions?  2) As long as I avoid these sites, there is no ongoing threat to my computer?

Thank you again for your quick response, and knowledge.  

[treed]

That is correct. Crypto-miners are not actually a threat to anything but your electric bill.

However, any site could potentially include a JavaScript to mine cryptocurrency. Although JavaScript runs in a sandbox with no access to anything outside the browser, the scripts can run automatically... if they couldn't, most of the web would become unusable.