[CentOS] OT: 1.1.1.1 is not private anymore?

Hi all,
Our network is suspected to be infected by malware by the detector in
upline network.
Turns out that some of our developers use 1.1.1.1 as a "pinging testing".

Google comes to my knowledge that 1.1.1.1 is not a private IP anymore?
Since when?
Also Google says 1.1.1.1 is well-known to be used by botnet command
and control host??

I've blocked it in the local gateway. Just curious......