The WorldCat search add-on does not save or hold any data. All searches are transmitted directly to WorldCat.org.
WorldCat may be used without registering, and if you choose to register, you may only do so directly from the WorldCat website.
Any registration or other data you transmit is a matter solely between you and WorldCat.

The WorldCat add-on will never record or possess any private data. No private data will be disclosed or used by the software in any way, especially not for marketing. If search data is cached on your computer or on a server anywhere, the WorldCat add-on is not responsible and will not retransmit or use that data in any way.