What is malware? It is short for “malicious software” and is a broad term that encompasses everything from annoying ad pop-ups to full scale viruses (that generally do not attack Macs).
Most commonly, and with a spike in frequency lately, Macs can get infected with spyware and adware that are generally limited to taking over your browser, re-directing your online surfing. The purpose of these pieces of software is to re-direct you to a site that is trying to extract money or information from you. The good news is that these are pretty easy to eliminate on your Mac without resorting to a full anti-virus software suite that will slow your Mac to a crawl (like McAfee, Norton, etc.).
I have received a lot of calls lately from people who seem to be stuck on a website that will not let them go to another website and/or is full of annoying pop-ups or re-directs that seem to lock their browser. Because modern versions of OS X browsers return you to your previously-visited websites, quitting the browser and re-opening it simply returns you to the annoying website. To have your browser “reset”, simply Quit your browser (using command-Q or right-clicking the Dock icon and choosing Quit or Force Quit), then start the browser again while holding the Shift key. This will point your browser to either your home page or a blank page and close all other tabs and windows. Problem solved (in most cases).
If quitting and starting the browser holding Shift does not work, perhaps you inadvertently allowed the installation of spyware or adware software onto your Mac (this is pretty easy to do if you are not careful about reading dialog boxes during an install). If this is the case I recommend you download and install the excellent & free spyware/adware removal tool Adware Medic. It was recently purchased by Malwarebytes, which is a legitimate company. They changed the name to "Malwarebytes Anti-Malware for Mac":
This is donation-ware so I encourage you to throw the developer some money if you like the software. This software only runs on your command so does not slow your Mac. It takes a few seconds for it to scan your system and remove the bad software.
DO NOT install software such as CleanMyMac, MacKeeper or the like. These pieces of software will slow your Mac and cause more problems than they solve. Look for them in your Applications folder and drag them to the trash. Soon after their uninstall program should start that will remove the other files these systems install throughout your Mac.
So, there you have it, your Mac is not allowing you to browse freely like you are used to, try these easy tips!