How to check for semicolon character in plan text file and if exists report an error message?

Hi,
using Vim 7.4 on Windows 7.

I have a plain text file and I would like to execute several commands from vimscript file, there are some :s[ubstitute] commands, nothing fancy.
But "substitute" commands should not be executed if there is at least one semicolon character ";" in plain text file.

So I need to do write something in the following logic:

if
one or many semicolon characters exists in plan text file
then
in status bar display error message: "Corrupted file. Please check for semicolon character."
and do not continue executing commands
else
do all that substitute commands.
end

Thanks

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