Websites Cop is a small tool which can monitor specified files on your website, alert you if there are any changes - a hacker has infected the site with something unpleasant, say - and automatically repair any damage by restoring the original files.
This isn't quite as straightforward as you might have hoped. The process starts by telling Websites Cop the files you'd like to monitor, for instance, and so probably what you'd like to do is point it at an entire folder of content (all file types are supported, not just web pages). But you can't: the program only supports your adding one file at a time, which may be tedious if you've a huge site.
Once you've told Websites Cop what you'd like to be monitored, though, everything else is surprisingly easy.
All you have to do is enter your FTP details (your site needs FTP access for Websites Cop to work), configure a setting or two - how frequently your files should be checked, whether it should send you an email if a change is detected - and you're done. One further click and the program will run in the background, monitoring your site and replacing altered files with the originals if any changes are detected.
If you have a website which is anything more than a simple personal page then it's wise to check that your pages haven't been hacked, just occasionally, and (once it's set up) Websites Cop makes this very easy.