A common misconception about Mac computers is that they are invincible to viruses, Trojans, or worms. Unfortunately, Mac users are just as vulnerable to viruses and malware as Windows users.
Mac users, like Windows users, surf the Internet, download software and files from websites and friends, and accidentally click on pop-ups, which are all common places for computer viruses to hide.
If your computer is running slow or you try to visit a website and you end up being redirected to another page, you may have accidentally downloaded a virus or malware software on your Mac. The first step would be to check your “Downloads” folder and see if there are any suspicious files that you do not recognize. Once you determine that, you may need to contact a computer professional for help in making sure all traces of the malware are removed.
It is also a good idea to ensure that your Mac only allows applications from trusted developers to be downloaded. To see if this is what you have selected click on System Preferences > Security and Privacy and General. Check that the option under “Allow Apps Downloaded From” is set to Mac App Store and Identified Developers or just Mac Developers.