Why Is My Mac So Slow? Can An Apple Computer Get A Virus?

I’m going to tell you why your Mac is running so slowly, clear up the confusion about viruses and Apple, and get you on the road to making your MacBook or iMac run like new. 

I was inspired to write this post after reading Beth H.’s question on Ask Payette Forward about why her Mac was running so slowly. She had been to the Apple Store and thought her computer had a virus because she was seeing the dreaded spinning rainbow pinwheel of doom more and more frequently.

The Apple employees told her Macs can’t get viruses and sent her on her way, but they left out a large part of the story – I’ll explain more in a moment. Truth is, Genius Bar appointments are timed and software issues can be difficult to diagnose, so the Genius Bar generally goes one of two ways:

  1. Erase your Mac and restore from a Time Machine backup (The Big Hammer – works some of the time by reloading your system’s core files, but issues can remain.)
  2. Erase your Mac, set it up as new, and then manually transferring back your personal data, documents, music, photos, etc. (The Really Big Hammer – pretty much a guaranteed fix, but it can be a big hassle.)

I’m going to walk you through a few simple steps to help you discover what’s slowing down your Mac and then get you on the right track for getting it fixed.

Can Macs Get Viruses?

The long and short of it is: Yes, Macs can get viruses, but you don’t need virus protection! That being said, when you’re seeing the pinwheel of doom and your computer is slow as dirt, there’s definitely something wrong.

So What’s Slowing My Mac Down?

When people think “computer virus”, they typically think of a malicious program working itself into your computer without your knowledge. Maybe you opened an email, maybe you went to the “wrong” website – but these types of viruses generally don’t exist for Macs, although there have been exceptions. When these viruses do appear, Apple squashes them immediately. Even while I was at Apple, I never knew anyone who had been affected by a virus like this, and I saw a lot of Macs.

Your Mac is vulnerable to a type of virus called a “Trojan Horse”, which is commonly referred to as a “Trojan”. A Trojan Horse is a piece of software that you download, install, and give permission to run on your Mac. Of course, this software isn’t called “Virus! Don’t Install Me!”, because if it were, well, you wouldn’t download and install it.

Instead, software containing Trojan Horses is often called MacKeeper, MacDefender, or some other software that promises to help your computer, while in fact it has the opposite effect. I’ve also seen websites that say you have to download a new version of Flash to continue, but the software you download isn’t from Adobe – it’s a Trojan. I’m just using these titles as examples – I can’t personally vouch for the quality of any individual piece of software. If you’d like to do some research for yourself, Google “MacKeeper” and take a look at what pops up.

Above all, remember this: Only download software directly from the company that makes it. If you need to download Flash, go to Adobe.com and download it from there. Don’t download it from any other website, and that goes for every piece of software. Download your printer drivers from hp.com, not bobsawesomeprinterdrivers.com. (That’s not a real website.)

Part of what makes Macs so secure is that software can’t just download and install itself – you have to give it permission to do so. That’s why you have to type in your computer password whenever you install a new piece of software: It’s yet another layer of security that asks, “Are you sure you want to install this software?” Nevertheless, people install Trojan Horses all the time, and once they’re in, they can be difficult to get out.

Macs don’t need MacKeeper, MacDefender, or any of those pieces of software that purport to speed up your computer. In fact, they usually slow things down or worse. MacKeeper is a Trojan Horse because you gave it permission to run on your computer just like any other piece of software you downloaded and installed.

If you haven’t installed any of the third-party software (or “bloatware”) on your computer, it could be any number of other things. Let’s take a look at a few:

Is Your Computer Out Of Breath?

Another thing to take a look at is Activity Monitor. Activity Monitor shows what background processes (those little programs that run invisibly in the background to make your computer work) are hogging up all your system resources. I bet you’ll see something spike the CPU up to 100% when you are seeing the spinning pinwheel of doom. Here’s how to check:

Open Activity Monitor by opening up Spotlight (click the magnifying glass in the upper right hand corner of your screen), typing Activity Monitor, and then clicking on Activity Monitor (or press Return) to open it up.

Click on the drop-down menu above ‘Show’ where it says something like ‘My Processes’ and change it to ‘All Processes’. This will show you everything that’s running in the background on your computer. Now, click right where it says ‘% CPU’ (the header of that column) so that it highlights in blue and the arrow is pointing down, indicating it is showing you what programs are running on your computer in descending order from what’s taking up the most CPU power to the least.

Which processes are taking up all your CPU? Also, click System Memory on the bottom to see if you have enough free System Memory. How many MB (megabytes) or GB (gigabytes) is free for programs to run on your system? If you find an application or process that’s hogging all your computer’s resources, there might be a problem with that app. If you can, try uninstalling it and see if the problem resolves itself.

Do You Have Enough Free Hard Drive Space?

Let’s check to make sure you have enough free hard drive space to work with. It’s a good rule of thumb to always have at least twice as much hard drive space free as you have RAM installed on your computer. In Apple lingo, RAM is called Memory. I have 4GB of RAM installed on this laptop so it’s a good idea to have at least 8GB of hard drive space available at all times. Apple built in a really easy way to check this out and I’ll walk you through it.

First, click the Apple menu in the upper left hand corner of your screen – look for the Apple logo to the left of the name of the program you’re currently using. Then click ‘About This Mac’. You’ll see how much RAM you have installed right there next to ‘Memory’. Now click ‘More Info…’ and click on the ‘Storage’ tab. How much free space do you have on your hard drive?

This is by no means a comprehensive list of everything that could be slowing down your Mac, but I hope this points you in the right direction. This post is undoubtedly a work in progress, but together, I’m sure we’ll identify and solve some of the most common issues that slow down Macs.

Thanks again for reading and I look forward to hearing from you!

All the best,
David P.

About Author

I'm a former Apple employee and the founder of Payette Forward, and I'm here to help you with your iPhone.

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Mike S
3 years ago

Great article Dave! Really helpful. I thought a Trojan was something else…….

4 years ago

I believe that this article and, especially, the one on fixing iPad battery problems, are the most clearly written and helpful online articles of any sort that I have ever encountered (yes, really, and I go back to 80 column cards and computers the size of a small apartment). Many thanks

Barbara Haddad
5 years ago

There’s an ad for MacKeeper on this very page!. :

David Morckel
6 years ago

What is kernal_task?

Patrick Moore
6 years ago

I am an idiot. I downloaded MacKeeper and now my iMac runs slower than molasses. Unusable. Currently trying to install updates and the little mouse has been spinning for twenty minutes…

Chris Gould
6 years ago

Hi David, is there an easy way to find and remove Trojans? I’ve had my Mac mini for several years and it’s quite possible that I’ve inadvertently installed something I shouldn’t have in that time.

You seem to be advertising MacKeeper on your website.

7 years ago

Dang it the descriptions really make me want to see if there’s potentially a program out there literally called Virus! Don’t Install Me! or something along those lines lmao

cristi kessler
9 years ago

In the middle of a lawsuit with a trustee who stole our father trust fund. last night I had a Doc flash on my screen at 1226am and then embedd itself in my Doc files. It is a falsified letter by this trustee dated in 2006. I have no docs that go back that far, since this same person erased all of my aol account emails in April 2014. Is this a trojan horse. How do I find who tis doing this and how do I save all my files for court and clean the trojan horse from my computer

Jared Cantor
9 years ago

Do you realize that there is a banner ad for Mackeeper directly below your article???? If that doesn’t definite irony I don’t know what does.

9 years ago

I guess I am missing something. I am desperate to find some solution to my slow Mac. WHile you mention a difference between the Mac having a virus or (more likely) Malware/3rd party stuff, you don’t mention what to do about it if it is on your mac or how to reliably find out since it is not recommended to use things like Mackeeper and such. Well then what should we do to get rid of possibility of Malware? Also, under the heading “Is your computer out of breath?”you mention the activity monitor. Well I followed the steps to open… Read more »

9 years ago

I appreciate the article and the questions, but I’m really not sure where your solutions are located. This is great, basic info but you said you’d help your readers “show you how to get your computer running like new again.” I think that’s a misnomer, unless I missed a page somewhere. Please correct me if I’m wrong. Thank you.

9 years ago

So I have found the thing that is taking up too much CPU on my parents computer. What can be done to stop it? It’s a background app.

9 years ago

Hello David, thank you for your post! I did the repairs and then I opened up my Activity Monitor. It looks like I have 4GB of physical memory with 3.95 of it used and 7.83 of virtual memory. I see that kernel_task is using the most followed by a bunch of Google Chrome Helpers (there are five of these running). I don’t know what to do now? Any advice and thank you!

9 years ago

you should read his article more carefully. most of what you referred to is simply wrong.

Coral Mansfield
9 years ago

My question is: what if I did authorize the installation of potential malware, i.e. A Trojan? (I stupidly authorized remote access to my MacBook to an online “tech support technician” to supposedly help me find a solution to a problem I was having with Microsoft word. And watched as they apparently checked out the problem.) Now the Microsoft word problem still isn’t solved, and I realize I may have invited malware. How would I find out if I did?/What would I do about it?

Kimberly North
9 years ago

Thanks David – the slowness was driving me crazy. Your instructions were so clear and I saw the speed improve immediately. I’ve saved your page for next time. Very kind of you to pay it forward!

10 years ago

Thank you very much for writing this article! The repair disk permissions seems to be the solution for my macbook pro (late 2008).

Anybody else have their iMac slow down over time? - FerrariChat.com
10 years ago

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