On the popular Discovery Channel program “Mythbusters,” hosts Adam Savage and Jamie Hyneman take a legend and deconstruct it to see whether its long-held beliefs are legitimate. They’ve busted all kinds of myths, from Jimmy Hoffa being buried under Giants Stadium (not true) to the ability to kill someone without a trace using an ice bullet (the bullet vaporizes as soon as the trigger’s pulled).

One tall tale they haven’t tackled is that Macs are impervious to malware, so you needn’t worry about cybersecurity solutions. Antivirus and anti-malware protection is for the PCs.

We’re here to bust that myth.

Growing trend

Out the gate we can tell you that it’s true, Macs don’t have the same problem with malware as PCs do. One of the main reasons: sheer numbers. Cybercriminals look at the market and see that the vast majority of folks are on PCs, so they concentrate their efforts on creating malware that will result in the largest return on investment.

But the tide is turning. Macs are now responsible for 7.5 percent of global personal computer sales. In the U.S., Apple is one of the top three PC vendors, just behind HP and Dell. And as creative departments grow in corporate environments (from design and content to programming and testing), more and more businesses are adding larger numbers of Macs to their environments.

The popularity of Macs leads to more cybercriminals wanting to write malicious code for OS X. Although still much lower than PCs, the number of threats targeting Apple operating systems has grown steadily, with a spike in Mac infections observed over the last 18 months. A recent study by Bit9 + Carbon Black found that the number of Mac OS X malware samples detected in 2015 was five times greater than in the previous five years combined.

Forms of malware on Macs

Apple security is fairly tight—OS X has a basic built-in anti-malware feature, and if the machine detects a malicious program, it gets added to the signature database. From that point on, that piece of malware can’t be opened on any Mac, unless the user has explicitly disabled security updates. But clearly some malware is getting through. Which forms?

The worst offender is adware. “There are many different adware programs infecting the Mac right now, and they’re in a constant state of flux,” says Thomas Reed, Director of Mac Offerings at Malwarebytes. “Adware-riddled installers are everywhere, and it’s becoming harder and harder to tell where a safe place is to download software.”

Other forms of malware have given Apple the slip, including Potentially Unwanted Programs (PUPs), Info stealers, Trojans, and even ransomware (KeRanger). While these forms of malware are less prevalent, they can still be quite dangerous. KeRanger was downloaded by around 6,500 people within the 12-hour period that it was available. Some of those users had their data completely destroyed.

How are they getting through?

The main way that adware and malware is getting through on Macs these days is through codesigned apps, using a certificate obtained from Apple. The certificate is either stolen or bought and simply treated as disposable, since it costs only $99. Apple can revoke these certificates if they see them being abused, and they do so quickly when they find a new signed malware. However, Apple doesn’t take a particularly hard stand against most adware, which can persist for a long time with the same certificate.

In addition, video and audio streaming sites and piracy sites often dole out adware. Software download sites distribute installers containing adware that has been added without the permission of the developers. Worse, even some developers’ own sites are guilty of bundling adware. For example, the popular Filezilla FTP client installs adware even when downloaded directly from the official site, and the free version of Avast had (and may still have) an ad-injecting feature in its browser extension.

What happens to your Mac after an infection?

Adware is a serious hassle. Injected ads are intrusive and can contain offensive content. They can also slow down your computer’s performance and result in browser destabilization. Malicious ads can even direct you to tech support scams where you can be scammed out of your money or into installing other harmful software.

But that’s not all, Bob! What else have you won? Info stealers can, obviously, steal your info. And in the case of ransomware, data can be totally destroyed with no shot of getting it back.

Final verdict

Myth: Macs are impervious to malware.

Fact: Macs, while less vulnerable than PCs, are assailable. Their security can be penetrated, especially by cybercriminals looking to deliver adware.

So do you really need a security solution for your Mac? “Although the primary threat right now is adware, it’s still a problem of epidemic proportions,” says Reed. “Even knowledgeable Mac users have been known to fall victim to some kind of adware, so it’s no longer true that you can avoid threats by simply being careful what you download.”

With increases in Mac popularity making OS X more appealing for crooks, plus the already considerable onslaught of adware, it makes sense to install an anti-malware program for your Mac. It should catch what OS X misses and restore your Mac’s performance to the high caliber you expect.

Now what other myths can we bust? Can tooth fillings really receive radio waves?