After working on some 50-odd Drupal projects over the past few years and inheriting a number of (often questionable) others, it occurred to us it'd be a good idea to have a script that detects hacks and/or "modifications" to Drupal core for a given Drupal install. The result is this remedial PHP script (or core agent) that detects your version of Drupal, downloads the appropriate tarball from Drupal.org, runs a diff on /modules, /misc and /includes, and returns you the results.