You can monitor the files on your website and be alerted if any modification was made without your knowledge.
As websites commonly have a large number of files, it's very tough keep track of each file, unless you have anything to help you.
This script reads a folder and calculates the hash for each file, on each run.
Then, it compares hash resulting files against last run. If anything changed, you will receive an e-mail and an alert file is creates on "alerts" folder.