dupdet is hosted by Wikimedia Toolforge.
Each request may be logged including URL of your tab and URL of your hyperlink.
These logs do not include any personally identifiable information.
These logs are subject to the Privacy Policy of Wikimedia Toolforge.
https://wikitech.wikimedia.org/wiki/Wikitech:Cloud_Services_Terms_of_use#What_can_and_can%E2%80%99t_be_done_with_user_information?

Here is a copy:

You should not collect or store private data or personally identifiable information, such as user names, passwords, or IP addresses (“Private Information”) from the individuals using your Cloud Services Project (“End Users”), except when complying with the conditions listed below. To avoid violating this policy, and to avoid causing confusion or misunderstandings for users, we recommend that you do not collect any Private Information. Only collect information if the purpose of the Cloud Services Project unavoidably requires such collection. If you do collect any Private Information, you must:

Clearly communicate to End Users a) that Private Information is being collected, b) how you will use it, and c) when you will delete it;
Inform the End Users that their information may be available to the Wikimedia Foundation, its volunteers, other Wikimedia Cloud Services users, or to the public;
Get express authorization from the End Users for the collection;
Hash, encrypt, or otherwise properly secure any Private Information you store;
Purge, anonymize, or aggregate any Private Information you store no more than 30 days after storing it;
Not share any Private Information outside of your Cloud Services Project; and
Not store any End User’s Wikimedia Project passwords.

Collecting any Private Information without complying with these requirements is a prohibited use and is grounds for account termination.