YouTube, Netflix, and a host of others have either made the shift to HTML5 video or use alternative technologies, like Microsoft's Silverlight. Thankfully, Flash is easy to remove and most of your favorite sites and Web services will continue to work fine without Flash installed. Though most exploits are targeted at Windows, Mac users are not invincible. Flash has become such an information security nightmare that Facebook's Chief Security Officer to sunset the platform as soon as possible and ask browser vendors to forcibly kill it off. Adobe has patched more than twenty Flash vulnerabilities in the last week- some of them days after active exploits were discovered in the wild- and issued over a dozen Flash Player security advisories since the beginning of this year.
TL DR- If you're running OS X 10.6 or later, download and run If you have OS X 10.4 or 10.5, use instead.
