Do I need an antivirus for a MacBook Air? If so which one?

Do I need an antivirus for a MacBook Air? 

The answer to that question is no but you can only recover from the effects of having installed and actually used the scam "cleaning" product by completely erasing the Mac.

Please read Effective defenses against malware and other threats - Apple Community.

Erase the Mac and reconfigure it from the ground up.

Rule 1 of Macs is don't install junk.

I understand. That is the reason that Mac must be erased and reconfigured from the ground up.

Merely removing scam "cleaning" products, even when performed in strict accordance with their uninstallation instructions, does not undo the damage they are capable of inflicting.

In fact the uninstallation instructions for "MacKeeper" product happen to be a model of uninstallation perfection. It works with nearly complete effectiveness, but removing it according to those instructions does not reverse its damage. Nothing short of erasing the Mac can accomplish that.

No need to apologize; I realize "erase and reconfigure" is a very brief way of describing how to recover from using "MacKeeper" or similarly categorized destructive products.

Recovery procedures can vary, but the following describes your options in detail. You will need to decide which procedure works within the time and effort you wish to devote to the task, including the possibility of using Time Machine to restore the Mac to a known, operational state, prior to the effects of having used those destructive products. Measures short of completely erasing the Mac are certainly possible, but they will be iterative (trial and error) and can be excessively time-consuming with no guarantee of success.

As a category, non-Apple "cleaning" products are scams. Merely uninstalling them, even when performed in strict accordance with their instructions (which often don't work) is usually an insufficient remedy due to the effects of having used them.

Very briefly stated, the recovery procedure from having used such things is as follows, and in the following order:

1. Back up the Mac using Time Machine or an equivalent backup strategy
2. Remove the scam "cleaning" products according to their instructions, and evaluate
3. Reinstall macOS using macOS Recovery, and evaluate
4. Reinstall all other potentially affected apps, and evaluate
5. Erase the Mac completely, followed by reinstalling macOS, followed by reinstalling essential apps from their original sources, followed by migrating User content from the Time Machine backup.

Since the results of Steps 2-4 are almost always unsatisfactory, I omit them as unnecessarily time-consuming. Step 5 is the nuclear option. An expanded procedure for it is provided below. Be sure to read everything and understand its implications. Less drastic solutions certainly exist, but this one will probably result in the least amount of your time and need for constant interaction. It is also unequivocally supported by Apple's published documentation, is what a Genius Bar would do if you were to pay them to do it, and it is the exact same procedure I use given a Mac that has been affected by similarly categorized products.

To recover from the effects of having used "MacKeeper" to modify your Mac, the additional software you require and the essential files you need, follow the applicable recovery procedure below:

• If you have a backup that you created prior to using MacKeeper, now is the time to use it. For Time Machine, boot macOS Recovery, and at the Mac OS X / macOS Utilities screen, choose Restore from Time Machine Backup. Choose a date preceding the installation of MacKeeper.
• If you do not have a backup that predates the use of MacKeeper, create one now. To do that read Back up your Mac with Time Machine.
  • The recovery procedure will require that you completely erase the Mac using macOS Recovery, and then create a new User Account whose contents will be empty. You will then be able to use Migration Assistant to migrate your essential documents including photos, music, work products and other essential files.
• To erase and install OS X / macOS read How to reinstall macOS.
  • Follow the instructions in that document under If you want to erase your startup disk, in Erase and reformat a storage device in Disk Utility on Mac.
  • Then, follow the procedure in Transfer to a new Mac with Migration Assistant.
  • When asked how you want to transfer your information, select Transfer from a Mac, Time Machine backup, or startup disk.
  • Under Select the Information to Transfer, select only your previous User account and do not select "Applications", "Computer and Network Settings" or "Other files and folders". De-select those choices.
  • Subsequent to using Setup Assistant, you will need to reinstall the essential software you may require, once again remembering to install software only from their original sources, and omitting all non-essential software.
  • "Non-essential software" is a broad category that includes but is not limited to third party "cleaning", "maintenance", and "anti-virus" products.

Phelopatir wrote:

John Galt wrote:

...

Then, follow the procedure in Transfer to a new Mac with Migration Assistant• .

When asked how you want to transfer your information, select Transfer from a Mac, Time Machine backup, or startup disk• .

Under Select the Information to Transfer, select only your previous User account and do not • select "Applications", "Computer and Network Settings" or "Other files and folders". De-select those choices.

So that means I lose all my word documents and such from my downloads and desktop, right? Guess that means I should store them in a USB since it's all my work that I need. I know I am asking a lot of questions but I am paranoid of losing my word documents and personal stuff from desktop and downloads.

Your Downloads folder, and even your Desktop, are folders within your user account (home) folder. So migrating that folder should migrate any word documents and other personal stuff stored there.

It would only be if you had multiple User accounts, or if you had stored some documents in system areas outside your User folder (which may be less of a possibility than it was with older versions of macOS), that there might be personal stuff outside your main User account.

However, if you want to be extra-careful (which never hurts when dealing with computers),

• Get a new external USB hard drive or SSD that's large enough to hold the contents of your internal drive. USB flash drives and memory cards would NOT be optimal for this purpose as they are easy to misplace and aren't always the most reliable devices for long-term storage.
• Format it, and use Carbon Copy Cloner or SuperDuper! to make a bootable clone backup of your entire internal drive onto it
• Unplug it and set it aside
• When you are restoring your Mac, migrate just your User account (as described above). I believe that it would not matter whether you migrated from your Time Machine backup or this bootable clone one (if both backups were current), but for the sake of simplicity, I'm assuming that you're migrating from the Time Machine one.
• If you find any documents missing after the migration, plug in the bootable clone backup. Do NOT start up from it (to bring the "cleaner", "antivirus", etc. programs back). Just simply mount it as an external disk, copy off the user documents that the migration missed, then eject it.

Once you are satisfied that the new Mac is set up properly, you could erase the new drive, and use to store a clone backup of the rebuilt system.

There is a third, and permanent method.

1. Click anywhere on a blank area of the desktop so Finder is the app listed next to the Apple logo at the top left.
2. Press, Command+Shift+H to open your user account Home folder.
3. With that folder still in the foreground, press Command+J
4. Click the check box for, Show Library Folder.

You only have to do this once, and the user account Library folder will now always be visible.

Phelopatir wrote:

John Galt wrote:

...

Then, follow the procedure in Transfer to a new Mac with Migration Assistant• .

When asked how you want to transfer your information, select Transfer from a Mac, Time Machine backup, or startup disk• .

Under Select the Information to Transfer, select only your previous User account and do not • select "Applications", "Computer and Network Settings" or "Other files and folders". De-select those choices.

So that means I lose all my word documents and such from my downloads and desktop, right?

No; that is the reason for migrating only the affected Mac's User Account. However, it is definitely a good idea to have redundant backups of work products and anything else unlikely to have been affected by those "cleaning" products.

Then, bear in mind that remedy can still fail to restore files within one's User Account that are nevertheless required by the system which those "cleaning" products may have removed and for which there will be no backup to restore. Restoring them presents a technical challenge for anyone not thoroughly familiar with macOS (you have to know which specific files it requires, create them in a format and location the system expects, with the proper permissions... etc). That's one time-consuming aspect.

This is what a typical User account directory looks like in Sequoia.

There is a user-level Applications folder, but typically there is not much in it. On my system, only one application placed anything there (and it wasn't a "cleaning", "antivirus", or similar application).

Most of the Favorites in the left-hand side of the Finder window are shortcuts to corresponding folders within the currently-logged-in User account. So I could get to Documents by selecting it – or by selecting the Home folder and then double-clicking on the Documents folder within the Home folder. Same place either way.

You have already seen how these apps can affect your computer's operations in a not good way. Apple's OS has its own built-in antivirus and its OS is locked so it can't be changed. An anti virus app simply takes your money for nothing in return. Remove it with the vendor's uninstaller app. Viruses do affect PC's, not Macs.

John Galt wrote:

5. Erase the Mac completely, followed by reinstalling macOS, followed by reinstalling essential apps from their original sources, followed by migrating User content from the Time Machine backup.

…

Step 5 is the nuclear option.

I would suggest that before doing this, the OP should have at least two backups of their user data – and that it might be good to back up that data in two different ways.

The idea is that you do not want to have all of the user data in one basket. Backups themselves can fail, and if there is only a single backup, and you wipe the original data, THAT is the moment that Murphy's Law says that your single backup is most likely to fail.

Backups themselves can fail, and if there is only a single backup, and you wipe the original data, THAT is the moment that Murphy's Law says that your single backup is most likely to fail.

👍

"Two is one and one is none."

I should add that there is another folder within your Home folder that you normally will not see in the Finder. It's a Library folder inside which many preferences and other user-level support files live.

Once this folder was as visible as any other. Then Apple decided to hide it. Now you can only get to this folder by going into Terminal or by holding down the Option key when using the Finder's Go menu. Normally you would not want to go there, but there are times when removing a particular preference file can be a solution to a problem.

Kurt Lang wrote:

There is a third, and permanent method.

… (description of one way of getting to View > Show View Options for the Home folder) …

You only have to do this once, and the user account Library folder will now always be visible.

I should have thought to check that!