Does 'chattr +i .bashrc' reliably prevent this? Always seemed sensible to me. Then again, there are a few files getting sourced by the shell and I am not sure I could spontaneously name them all.

The attacker could use `chattr -i .bashrc` with the same privileges before editing your bashrc. A better way would probably be to use `sudo chown 0:0 .bashrc`.

Also you will want to do the same to .profile (because of LD_PRELOAD etc). And also do the same to any directories in your $PATH (~/.local/bin etc)