Hi,
check your vCenter alarm, if someone added an action for the "Host CPU Usage" alarm or if there is another defined.
It might trigger such a nonsense action after 5 minutes over 90% if someone configured it that way 
Also log onto the ESXi server with ssh or via console and check the logs:
/var/log/auth for login
/var/log/shell.log for commands that were sent on the shell.
Tim