IS EL CAPITAN going to remain secure ?

[Retromac2008]

is it still secure and supported?
how long is it going to remain secure?

 

[KALLT]

It is likely supported till autumn 2018.

 

[ardchoille50]

is it still secure and supported?
how long is it going to remain secure?

It is still supported. How long it will remain secure is anyone's guess. Since vulnerabilities are neither intentional nor public knowledge until they're discovered, there is no way of knowing how long any software will remain secure. The only secure computer is one that is never powered on.