Command not allowed from exrc/vimrc in current dir or tag search

When opening a file with vim, you encounter errors like the following:

This may happen in the following situation:
- the file you are trying to edit is in /home/user/myfile.txt
- the file /home/user/.vimrc exists.
- you are logged in as 'root', not as 'user'.
- as root, $HOME is set to /root.
When you start vim, it will source /root/.vimrc then it will try to source the .vimrc in the current directory, i.e. /home/user/.vimrc.
Even though you are root and have the permission to edit the file, security settings in vim causes the warning to appear.

You can ascertain which files are being sources and processed when vim starts by using the -V flag. Study the output:
# vi -V myfile.txt

Solution 1) Do not edit the file as root. Edit it as a regular user.
Solution 2) cd .. ; vim user/myfile.txt
Solution 3) chmod 600 .vimrc # prevent other users from loading the .vimrc that does not belong to them.