I see your tail

In Microsoft Windows 7 Professional one may use a MAK (Multiple Activation Key) to activate an install.  Now, if one loses a "normal" key it can be retrieved from the system using a myriad of key viewer programs. Something to note, however, is that as soon as activation completes using an MAK the key is deleted and so there is no way to retrieve it. But, if all you need to know is which key of several was used then the command slmgr –dli will show the last 5 characters of the MAK used to activate.