How can I validate my downloads from the Internet?
Mac OS X 10.4 Tiger includes download validation. Several Apple applications use this feature to provide additional checking for content obtained from a network. If you open an attachment in Mail, and it is actually an application rather than a document, Mac OS X’s download validation will warn you about unsafe file types, and you should cancel if you have any doubts about the file. If you save an attachment or drag it to a folder, use the Finder to inspect it as described above. If you were expecting a document, but the Finder indicates you received an application, do not open that file. Instead, delete it immediately.
If you navigate to a downloadable file with Safari (for example, by clicking a download link, Mac OS X’s download validation will warn you about unsafe file types, and you should cancel if you have any doubts about the file. If you download a file by Command-clicking or selecting Download Linked File from a contextual menu, it will not be inspected by Mac OS X’s download validation and it will not be automatically opened. You should inspect the downloaded file using the Finder as described above. If you were expecting a document and Finder indicates that it is an application, do not open that file. Instead, delete it immediately.