Mac adware is bad. Windows is worse. Who's to blame? Free software download sites.
As we've shown before, if you make the huge gigantic mistake of trusting CNET Downloads, you could already be infected with this type of adware. Two of the top ten downloads on CNET (KMPlayer and YTD) are bundling two different types of HTTPS-hijacking adware, and in our research we found that most other freeware sites are doing the same thing.
Reagan had the old Russian proverb right: Trust, but verify. Gatekeeper makes this much easier to deal with on the Mac by preventing you from running apps that don't come from signed Apple developers. Advantage: Mac. If you want to stay even safer, just buy apps from the Mac App Store. If you're not careful, it's really easy to catch an adware injection from sites where you might not expect it.
Unless you do something stupid like pirate Mac apps, that is. In which case you deserves what happens to you, jerk.