Old versions of MS Office applications
Microsoft Word 2.0, 6.0 and 95 (7.0), Excel 4.0, 5.0 and 95 (7.0) are using even less powerful encrypting algorithm. To encrypt a document, an exclusive OR operation (XOR) with a sequence derived from the password is being used. As some (predictable) auxiliary information is encrypted, too, that sequence can be recovered. So, file open password in these Word and Excel versions can be retrieved in a fraction of second.
Applications for password recovery:
Advanced Office 2000 Password Recovery
Advanced Office 95 Password Recovery
http://www.elcomsoft.com