TuxTraining

Most distributions use Bash as its default shell. One of the features of Bash is its ability to keep a running history of commands the user has typed. This could, however, end up being a security problem. If a bad guy were able to compromise a user’s home directory, they could view commands the user has executed. In some cases, this could expose improperly used passwords or special privileges available to the user (such as sudo.)
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The following changes following file permissions, so that nobody can change the account privileges:

chattr +i /etc/passwd

chattr +i /etc/shadow

chattr +i /etc/group

chattr +i /etc/gshadow

See here for further details of the chattr command