Apple still sells OS X Snow Leopard.
Apple isn't issuing any security updates for it, any longer.
But this does NOT mean OS X Snow Leopard is obsolete.
I still use OS X Snow Leopard as my regular working OS X version as it is a superior OS X version, in every way, compared to OS X versions that have come after it.
Especially since the post Steve Jobs versions of OS X.
If you are worried about security issues with OS X Snow Leopard,
Ditch ALL Googlewares. They are ALL a serious resource hogs on the OS X system.
The additional benefit is that you'll stop Google from mining your data when you surf the web
https://support.google.com/chrome/answer/95319?hl=en
https://support.google.com/drive/answer/2375081?hl=en
If you do not like Apple's Safari web browser, download, install and try Mozilla FireFox, instead.
http://www.mozilla.org/en-US/firefox
The current, up-to-date version of FireFox is fully compatible with OS X and is regularly updated by the great developers of the Mozilla group.
I have, also, stopped using the Google search engine regularly (due to Google's privacy policies or lack thereof) and I now use DuckDuckGo as my default search engine.
Also, since it appears you are reluctant to use the Etrecheck report support software to help aid in troubleshooting your Mac, we are going to have to do this the hard way to get to your Mac issues.
To find out info about your system,
Click on the Apple symbol in the upper left of the OS X main menu bar. A drop down menu appears. Click About this Mac. A smaller popup window appears. This gives you basic info like what version of OS X your iMac is running, the speed of your iMac's CPU and how much RAM is installed.
Click on the button that says More Info. A larger window appears giving you a complete overview of your iMac's hardware specs.
Highlight all of this info and copy/paste all of this into another reply to this post, editing out your iMac's serial number before actually posting the reply.
This will tell us everything about your iMac so we may begin to help with your iMac issues.
How much RAM installed on your Mac?
How full is your Mac's hard drive?
Locate your iMac's hard drive icon on the OS X desktop. Click the icon once, then use the keyboard key combination Command-I. This will give you additonal info about your iMac's internal hard drive.
How many applications do you run simultaneously in the background while working in another application?
If you have a long list of user login/startup items that launch at startup/login, you need to reduce the amount of these to less than 6 or so items or less, if possible.
Do you have any unnecessary antivirus installed on your iMac?
Do you have any unnecessary "cleaning" apps on your Mac like MacKeeper, CleanMyMac, TuneUpMyMac, MacSweeper, MacCleanse and the like installed on your Mac?
Have you updated all of your installed software and updated all connected third party device software and drivers?
Have you updated all of the various web browser plugins you that have installed within your web browser?