What is adware?
Hey! Do you want to lose 15 lbs. in 15 days? Click here for the amazing secret! (Close window.)
How about this juice cleanse? (Close window.)
You’ll never have to eat solid food again! (Close window.)
Looks like you might have a virus. Install this antivirus solution now! (Click.)

That. That’s adware. Adware is unwanted software that is designed to display advertisements, usually within a web browser. It uses shady methods to either disguise itself as legit or piggyback on another program to get installed on your computer. Once installed, it changes the way your browser behaves by injecting ads into web pages, causing pop-up windows or tabs to open, and changing your home page or search engine.

What does adware do?
The people who create adware do so in order to make money. Plain and simple. While legitimate software applications do use online advertising, the ads are typically bundled within the program and designed and displayed in ways that the developer specified. Adware does its own thing. Whether you download it without full knowledge of what you’re getting or whether it attaches itself onto legitimate software like a tiny tick hiding in your sock, it’s behaving in a way that neither you nor the software it latches onto wants. Once on your computer, it sucks up funds made by clicking on the ads, which are paid for by advertisers who either knowingly or unknowingly hire the adware company to distribute them. Does it steal your money? No. But it’s suspect, nonetheless.

Who makes adware?
The first appearance of adware for Macs was in 2012. Since then, more than 25 different forms of adware have popped up in the wild. The makers of adware are sometimes doing so behind closed doors, working as professional black hat hackers or with organized crime units. But usually, they are hiding in plain sight, operating as actual corporations who claim to sell software on the level. They get away with it because their adware is often hidden in the fine print of a long installation agreement that most people skip over. So technically, they’re not doing anything illegal. You accepted the terms of the installment, so they can go ahead and spam you all they want.

Where does it come from?
Adware for Macs always comes in the form of a Trojan horse. What’s that? Glad you asked. Trojan horse malware works in much the same way as the Trojan horse of Greek mythology. It promises you one thing, but delivers another. And what these Trojan horses deliver is adware.

A Trojan horse containing adware may pretend to be something you want, such as a video plug-in or player, but what you really end up downloading is an adware installer. It may hide inside a legitimate download from an unethical site. Often, it shows up in downloaded files from torrents or piracy sites.

What’s the difference between adware and other forms of malware?
Adware and malware are not quite the same thing. While adware is a form of malware, it differs from malicious software in that it’s not conducting particularly evil activities such as keylogging or holding files for ransom. Because of this, most antivirus (AV) programs don’t bother to detect adware, and if they do, they don’t do a very comprehensive job. AV software might flag adware as a potentially unwanted program (PUP), but it will not remove it.

How can I protect myself against adware on a Mac?
While the newer operating systems on Mac OS X have cracked down on malware, they do not protect you against most adware. This means that if you want to keep adware from clogging up your system and slowing down your computer’s Internet connection, you’re going to have to take a few precautionary steps.

First, practice safe browsing habits. Avoid torrent sites, illegal downloads, and pay close attention to any software that you download. In addition, beware of opening applications from unknown—or even known—sources. If Great Aunt Cathy forwards you a chain letter written in blue Comic Sans with an attachment that reads “Open right meow,” you might want to avoid opening it. Finally, download an anti-adware or anti-malware program for your Mac.

So what’s the lesson learned here? Adware is proliferating on Macs, and while it’s not a problem that will destroy your computer or hijack your files, it will annoy the heck out of you and make your Internet surfing experience a lot less fun. So arm yourself with knowledge and take the necessary steps for an adware-free existence.