What is MacKeeper and should I delete it from my MacBook Air ?

Also, if you got it while "downloading other things" you may want to consider in the future where you download things from. The best options are the Mac App Store and the developers' own websites. Third party aggregation sites are frequent sources of the type of problem you are having.

How to delete Mac keeper malware manually .

Enter in System Library - Click on finder and take cursor on top menu bar , click on Go > computer > Macintosh HD

( a ) Applications - Mac keeper app

Click on library .

( b ) Launch Daemons

com.mackeeper.AdwareAnalyzer.AdwareAnalyzerPrivilegedHelper.plist

com.mackeeper.Mackeeper.MackeeperPrivilegedHelper.plist

( c ) PrivilegedHelperTools

com.mackeeper.Adware.AdwareAnalyzer.AdwareAnalyzerPrivilegedHelper

com.mackeeper.Mackeeper.MackeeperPrivilegedHelper

Enter in User Library - click on finder > Go > hold option key > Library , these are the locations where malware hide .

( a ) Application Support

Folder - com.mackeeper.AdwareAnalyzer

Folder - com.mackeeper.MacKeeper

Folder - com.mackeeper.Mackeeper.Mackeeper.Helper

Folder - Mackeeper - and its subfolder - statistic 2

Folder - Mackeeper 3 - and its subfolder - NE notifications

( b ) Launch Agents

Folder - com.mackeeper.AdwareAnalyzer.plist

Folder - com.mackeeper.Mackeeper.Helper.plist

( c ) Logs - Mackeeper.log

Mackeeper.log.signed

( d ) Preferences

com.mackeeper.AdwareAnalyzer.plist

com.mackeeper.Mackeeper.Helper.plist

com.mackeeper.Mackeeper.plist

( e ) Saved Application state

com.mackeeper.Mackeeper.savedstate

( f ) Caches

Folder - com.mackeeper.AdwareAnalyzer.plist

Folder - com.mackeeper.Mackeeper.Helper.plist

Folder - com.mackeeper.Mackeeper

These folders / subfolders and related .plist are dragged and dropped to the trash .

Also if the app is in download folder it is moved to the trash .

Restart the Mac from apple logo and empty the trash .

Yes, if you can. It has a horrible reputation.

You may have difficulty getting rid of it. If so, one method is to use Malwarebytes: Free Cyber Security & Anti-Malware Software | Malwarebytes