I am not native English speaker so sorry for misunderstandment
I didn’t say it’s overall better
I said even though on base level OpenBSD is much more clean and secure than Linux it lacks or lags behind Linux in adding mitigations for security vulnerabilities
And there are far less eyes on OpenBSD so many vulnerabilities don’t get discovered in first place
Any software can be malicious even essential ones just look at recent Xz vulnerability (And it was discovered by sheer chance), OS should have systems in place like proper sandboxing, permissions (Not half baked one like flatpak) …
No good solution but easiest thing to do is System monitor resource usage (CPU, GPU, Memory) check it when programs are closed and system is idle
Captcha is probably unrelated to botnet, it can be from your browser (most privacy focused browsers like LibreWolf, Brave, Hardened Firefox get this captcha problem) or your VPN/proxy if you use one