How do I check my MacBook Air for Malaware , Adware , Virus without down loading a App ?

Go to system preferences and click on users and groups open the pad lock by entering admin name and password ( in case if it is an admin account ) , select login items , if you see app select it and click on minus sign to get deleted .

In system preferences itself click on Security and privacy , click on Accessibility then privacy select the suspicious app click on minus sign to get deleted .

Click on finder and search in Applications and download folder . 

The next step would be enter in System Library .

Click on Finder , take cursor on top menu bar click on Go - Computer - Macintosh HD - Library 

You have to manually search malware in some folders where they reside .

1.Application Support 

2.Caches 

3.LaunchAgents

4.LaunchDaemons

5.Logs 

6.PriviledgedHelperTools

7.Startup-items

8.Receipts

9.Preferences - the plist of malware is to be removed , if there is com.apple .xxxx .plist it could also be com.apple.xxx.plist 

10.Extensions

11.Frameworks

12.internet Plug -ins

13.Input Methods

14.ScriptingAdditions

Then enter in User library ( click on finder and take cursor on top menu bar , hold option key and click on library ) .

Search in folders 

1.Application Support 

2.Caches

3.Cookies

4.Safari

5.Logs

6.Saved Application State

7.LaunchAgents

8.Internet Plug -ins

9.Input Methods

10.Preferences - com.apple.xxx.plist .

11.Containers are also to be checked .

Then again click on Finder - Go - Macintosh HD - System - Library - Frameworks - search the malware remnants in Framework folder .

Right click on remnants from the above folders and move to the trash bin , restart the computer and empty the trash .

Protect your Mac from malware - https://support.apple.com/guide/mac-help/protect-your-mac-from-malware-mh40596/mac

If you want to scan you will have to use thir party software. Malwarebytes if often recommended for this. For a manual scan you can use the free version.

It's not at all unusual for software updates to result in slow performance, but the effect should be temporary. For example the need to rebuild caches or databases required to maximize performance will be burdensome for a length of time that's difficult to predict. Once those housekeeping tasks are complete, which can take a number of hours, your Mac should work faster.

Whenever a Mac is not performing as well as expected it would be anyone's natural inclination is to ask "what's it doing". The very first place to look for that answer is Activity Monitor. Read about it here: How to use Activity Monitor on your Mac - Apple Support. Any app or process using more than (very approximately) 10% CPU is worth investigating. When one or more of those apps approaches 50% CPU (again, a very approximate number) the effect will become noticeable.

Some apps are very memory-intensive, and their demands may exceed the amount of physical RAM installed. Again it's very easy to determine if a Mac's performance is being limited by available memory: if Activity Monitor's "Memory Pressure" graph is frequently "red" your Mac would benefit from additional memory. If not, it won't. It's literally that simple.

clifford267 wrote:

Thank You Experince has taught me never down load anything I know nothing about,

I have learned from that same experience.

If the very first place to look for potential problems is Activity Monitor, the very last place to look is for some magical cure-all.

There is never a need to download or install anything to diagnose a Mac, or to correct a problem resulting from downloading or installing whatever may have caused a problem to begin with. macOS already includes all the utilities you need. On the other hand if you go in search of a magical cure-all, you will find an abundance of shrill opportunists and parasites eager to exploit you. You don't have to play that game.

Well there is an alternative method, I just didn't think you wanted to go there. Kind of like you asking, "How do I build a 10 story building without a contractor?" and we tell you to go out and buy a bunch of bricks, cement, a trowel, a bucket and a ladder...

clifford267 wrote:

How do I check my MacBook Air for Malaware, Adware , Virus without down loading a App?

Start by describing what's wrong with your Mac: why do you perceive something like that exists?

It's not at all unusual for people to assume their Mac is affected by something unwanted. For example, something weird happens, as is certain to happen with anything from time to time. Unfortunately the assumption such weirdness was the result of a "virus" often leads into downloading and installing some garbage product claiming to fix everything that could possibly be wrong, with the click of a mouse, "for free". Then, their initial assumption becomes a self-fulfilling prophecy.

Actually Malwarebytes is frequently recommended here. Apple never officially recommends third party software but several people have reported going to a Genius Bar with malware issues and being told to use Malwarebytes. Apple does not include it on the App Store because it does not comply to certain restrictions which is has to violate in order to chase malware to where it installs itself.

Now if you had been asking about which virus scanner to install we would have given you a definite "do not".

I could not resist posting John Galt's article, Effective defenses against malware and other threats…

clifford267 wrote:

... took it too Best Buy who fried the computer.

I hope you learned from that experience too. Nothing good ever comes from setting foot inside a Best Buy.

Malware bytes anti malware for Mac is very effective and you scan the Mac after few days ( make sure updates appears for the app , install them ) and it's very much compatible with Mac .