Summarize this article:

All modern Macs come equipped with their own built-in malware protection. If your system is not configured to receive regular updates, malware can slip through the cracks. Click “System Preferences” in the Apple menu, then click “App Store,” and make sure the following two options are checked:  Automatically check for updates Install system data files and security updates If you’ve installed MacKeeper and are receiving pop-up messages claiming you have a worm virus, do not follow their links or enter your credit card information. MacKeeper is known malware and should be removed from your system. Because there are no Mac “viruses,” it’s likely that a suspected worm virus is actually a different form of malware, like adware (excessive and tricky advertisements) or ransomware (software that holds your files hostage until your credit card information is provided). Regardless of its type, you’ll want to remove it from your Mac.  Malwarebytes Anti-Malware for Mac and Sophos Antivirus for Mac will both scan for and remove all adware at no cost. There are many paid options to scan and remove malware from Macs, but they are not typically recommended by experts. Start your anti-malware program and find the link that says “Update” (or something similar). Before running a scan, you’ll want the program to have up-to-date malware information. The actual name of the button will vary depending on your anti-malware program. The scan will take several moments to complete. If the program finds malware, follow any prompts to “quarantine” the rogue files. This will remove them from your system without sending them to the Trash. To keep your computer free of malware (including worms), Apple recommends taking certain precautions when using the Internet.  Never open e-mail attachments unless they were sent from a legitimate source. Limit downloads to the Mac App Store and identified developers. Mac checks all apps on its App Store for viruses and trusts other developers registered with Apple. To configure this feature on your Mac, select “System Preferences” from the Apple menu, click “Security & Privacy,” then “General.” There, select “Mac App Store and identified developers.”

Summary:
Make sure your Mac is up-to-date. Uninstall MacKeeper. Download and install an anti-malware program. Update your anti-malware software to the latest definition files. Click the “Start Scan” or “Scan Now”. Quarantine your malware. Avoid malware in the future.