The older Secure OSX ?

No, it is not secure. There are numerous, publicly-known vulnerabilities in Snow Leopard. I would not use it.

 

What follows is my opinion only, and I realize that it "goes against the grain".

If you need to install Snow Leopard because it has something in it that you like or need (to run older software, for example), just do it and don't worry about it.

Just a week ago I retired a 2010 MacBook Pro that came with Snow Leopard. I continued to use it as the "regular OS" on that machine for it's entire service life of almost 7 years.

Ran great, never a problem.
"Security" was never an issue for me.

Again, my opinion only.

 

Well, clearly, internet security depends on the kind of internet browsing you do. Sticking to major sites will likely not cause any problem with even modest security measures.

 

If you visit sites that display ads or load any sort of third party tracking javascript, you are at extreme risk for eventual infection. Same goes if you check email. Installing and maintaining a local HOSTS file like https://github.com/StevenBlack/hosts will help, by preventing your machine from ever loading content to many known bad sites.

And never, ever install Flash or Java.

 

You're exaggerating the risk. There are few to no malware programs out there for any OS X version, and while Apple may no longer be patching holes in Snow Leopard it has a less than one percent market share now so there is no incentive to use any known exploits. The calculation may be different if you are doing something that would be a high value target where a hacker would expect to get their money back for the time it takes to get in.

 

Sure it's fine to use it, with up-to-date browser/email client software like the very latest release of Firefox ESR 45 and only download from trusted sources. I would not recommend using it as your main OS if you're concerned about security, but known exploits in such old software are rarely targeted anyway.

PowerPC Leopard, despite being even older and still vulnerable, is less likely to be exploited due to all the effort this would take for a very small percentage of overall users.

--- Post Merged, Dec 6, 2016 ---

Good advice for the latest MacOS, not just older ones.

 

You underestimate what a cesspool of automated hostility the internet is. I deal with securing systems and networks full time. I will never permit any device to connect directly to the internet. It has to be fully patched and behind a firewall with content filters. Only then does the risk of getting hit with a driveby attack drop to "it's probably going to be okay."

 

You may be overestimating the effort. Snow Leopard has many publicly-known vulnerabilities. They have some of the work, if not most of it, cut out for them. Not all exploits need to be complicated or be done for maximum impact, there are some rather trivial vulnerabilities in Snow Leopard that even less-experienced hackers can exploit. You are also running out of options for secure web browsers. Snow Leopard has not seen security updates for more than five years now.

It should be common sense to use a patched operating system. Technology moves on. Snow Leopard does not even have Gatekeeper or full-disk encryption.