How to disable exec service in AIX
This service is design to allow users of a network to execute commands remotely. However, rexecd does not provide any good means of authentication, so it may be abused by an attacker to scan a third-party host. This entry should be disabled, as there are numerous secure alternatives for this service.

In my case, service was open and I have comment it out as shown below:
nimserver# vi /etc/inetd.conf

nimserver# cat /etc/inetd.conf |grep rexec
# exec    stream  tcp6    nowait  root    /usr/sbin/rexecd        rexecd
nimserver#

Restart the inetd services
nimserver#refresh -s inetd

I test it using X-windows session “Humming Bird Exceed Open Text” by lunching the REXEC session as shown below:



How to Disable Telnet on AIX 6.1
Edit and comment out telnet. As an example it will looks like

lpar2#vi /etc/inetd.conf 

#telnet  stream  tcp6    nowait  root    /usr/sbin/telnetd      telnetd -a

Now refresh the inetd daemons
# refresh -s inetd

You should get an error message like this:
lpar1 #telnet lpar2
Trying...
telnet: connect: A remote host refused an attempted connect operation.
lpar1 #

Done…