We have helped a few customers recently who have inadvertently installed malware or spyware after visiting a website or receiving a call pretending to be Apple. They were advised their Mac was locked, slow or infected by a virus. To resolve they need to pay for support and/or to install software.
No they are no the latest Bond movies! Sadly they are new security issues affecting a performance feature of modern CPUs called speculative execution.
Should I be afraid?
A little bit, it is one of the more serious issues that Apple has had with macOS. Anybody who has physical access to your Mac or can get to it through via screen sharing, VNC, or remote desktop can gain complete access to the machine.