Most of the answers seem to suggest this is some sort of tracking or malware. It is not but you still shouldn't be seeing it. That is only suppose to be seen by Yahoo employees and the internal links are there so they can report bugs easily. It's also present on betas but shouldn't been seen on the outside. It looks like somebody messed up and let it go to prod without having an employee check.
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https://www.google.com/search?q="Y%21+Confidential"
Certainly lots of very confused people keep seeing it.
Most of the answers seem to suggest this is some sort of tracking or malware. It is not but you still shouldn't be seeing it. That is only suppose to be seen by Yahoo employees and the internal links are there so they can report bugs easily. It's also present on betas but shouldn't been seen on the outside. It looks like somebody messed up and let it go to prod without having an employee check.