umask setting on a logon script

hi, am new to AIX.
i have an issue. iam asked to change the umask setting on a logon script on a server to prevent writable files. i logged in as the root user and typed in umask and it displays 022, which i believe is 755 for direc and 644 for files.
1) how to I identify where the logon script for the server is?
2) what umask should i put to prevent "world writeable files"(it said world writeable files)

replies would be very much appreciated.
thank u everybody for ur help.
karthik

edit /etc/security/user file and set umask = 027 under default configuration

thanks very much for your help