I checked in settings and the problem is i not have any update available for my phone , last security update 1 February 2019. When i press search say not any available, what i can do?
Over a year with no update is likely that devs stop working on updates or already reached the possible updates that can apply to your phone model. That's normal even for the latest model and to verify this you need to interact with their community. In most cases, it should have an announcement. Try searching for your phone's community in XDA.
Old devices might never get an update as well,so if you can afford a new one just go for it with latest oxygen version so you will be safer to the vulnerabilities as long as you verify any apps before installing.
Well, the problem is not old device, it still works ok but who know, they have problem with Google and not receive any further update. You reffer me to install a custom OS?
Actually, either you are using Stock or Custom ROM, it doesn't matter with regard to security. Just take note of the basic things needed regarding the security of your phone. Malware or any type of harmful and malicious software will not be triggered automatically unless the user will execute it, maybe because they don't have an idea of what they are dealing with.
The majority of Custom ROM doesn't really upgrade you into the genuine version of an updated OS. It was ported to feel the experience of having an updated OS while at the same time, tweaking your phone model performance by removing bloatware and adding some enhancements. It also gives you the ability to modify CPU performance by overclocking and allowing you to install a Custom Kernel.