Often times clients that are already running Magento are not aware that their core Magento files have been modified.
Desecrating Magento core files is punishable by death. So here is a little tip on how to quickly scan the core and see if someone needs to be hanged publicly or not:
diff -qrbB default_sacred_core_folder clients_core_folder
To explain the options lets take a look at man pages:
report only when files differ
recursively compare any subdirectories found
ignore changes in the amount of white space
ignore changes whose lines are all blank