iMac 27" late 2013 way too slow

Hi samira61,

Thank you for the EtreCheck report. In your report, it says MacKeeper is installed. This is bad malware. There are two ways to proceed:

1. Download Malwarebytes. It will clean up your Mac. Malwarebytes is a free and trusted macOS Anti-Malware.
2. (What I would Do) Erase and reinstall macOS. This will solve all your issues, probably even the slow performance.

If you are going to proceed with option 2, understand EVERYTHING will be erased. Please create a backup, but I would not reccomend backing up with Time Machine, as you have Malware. Time Machine could potentially just backup the Malware. Use iCloud or copy and paste data manually to an external hard drive.

1. Backup all DATA! When you do this, all your data will be erased! This action cannot be undone! Make sure your are comfortable with where your data is stored besides the Mac. In this case, since you have Malware, use iCloud or an external hard drive, and copy and paste data. See this article How to back up your Mac - Official Apple Support
2. Go to System Preferences, and then Apple ID. Turn off Find My Mac, then sign out of your Apple ID.
3. Restart the Mac, then when you hear the startup chime, or the screen lights up, immediately press and hold Option + Command + R. Option + Command + R will give you the latest and greatest macOS that your Mac can support. 
4. Once you are in macOS Recovery, verify you are connected to a WiFi network in the top right corner, and verify your are in macOS Catalina Recovery. You can tell by the "Reinstall macOS" logo.
5. Then go to Disk Utility.
6. Click the “View” button in the top toolbar and select “Show All Devices.”
7. Select the main hard drive name, not your volumes. For example, select APPLE HDD, APPLE SSD, or Fusion Drive instead of “Macintosh HD.” It will be the top item.
8. Click erase, and input the following EXACTLY:

Name: Macintosh HD

Format: APFS

Scheme: GUID Partition Map

Click Erase

Now, let's reinstall macOS.

1. Quit Disk Utility.
2. Open the macOS Catalina Installer.
3. Follow the on-screen instructions and select Macintosh HD as your disk to install to.
4. Let the process finish, don’t restart, sleep, or shut down your Mac. Also don’t disconnect from WiFi.
5. Let the process finish; then setup your Mac, and restore your data. For iCloud data, sign into your Apple ID and download data from iCloud. If you copy and pasted your data to an external hard drive, copy and paste the data back. 

I hope this helps!

Cheers,

Jack

Start by uninstalling MacKeeper. Active-scanning 3rd party security software always slows system performance by sinking hooks in to monitor activity, and the built in MacOS security is good enough that most users don't need it.

Tip: use the developer's uninstaller or uninstall instructions. Simply dragging to trash may leaves secondary pieces still running.

Second your hard drive is running unusually slow. If uninstalling MacKeeper isn't enough you may wish to reinstall MacOS onto an external USB 3 SSD.

Yes, MacKeeper is a major issue. It was so bad that, when the Russian developers could not sell enough, they started sneaking it onto computers using adware and clickbait. Rather insidious.

My concern is your hard drive:

Performance:

System Load: 2.41 (1 min ago) 1.79 (5 min ago) 1.43 (15 min ago)

Nominal I/O speed: 1.62 MB/s

File system: 31.95 seconds

Write speed: 48 MB/s

Read speed: 64 MB/s

We have a 2011 iMac with the same drive specs (7200rpm; 3GB/sec bus) and its write/read speeds are much higher:

Performance:

    System Load: 1.62 (1 min ago) 1.67 (5 min ago) 1.87 (15 min ago)

    Nominal I/O speed: 0.05 MB/s

    File system: 38.28 seconds

    Write speed:  112 MB/s

    Read speed:  91 MB/s

Yours should be able to make those speeds. It still will not be super-speedy but will be better than it is today.

If is very possible that MacKeeper is dragging down drive performance. I have seen it before with other useless utilities. Post a new report so we can see if MacKeeper is fully ejected and we can also see if that helped the drive performance a the same time.

The 2012 and newer iMacs are very hard to service/upgrade internally due to a sealed-case design. If evicting the scamware does not help, we still have another option to offer.