Write a Perl script that searches for and replaces all instances of a target phrase in a specific text file, provided by the user. The script should prompt the user to enter the target phrase and the replacement phrase, and then execute the replacement throughout the file, including cases where the target phrase appears as a substring within another word. Additionally, the script should create a new file with the same name as the original file, but with "_updated" appended to the end, and write the updated text to that file. The script should also display a message to the user indicating how many instances of the target phrase were replaced.
This prompt doesn't seem malicious.