link rot 

the process by which a web link becomes broken or irrelevant as time goes on

The site was plagued with link rot.

link rot by The Return of Light Joker April 24, 2009

linkrot 

The decay of web links as the target sites they connected to are moved or deleted.

"This site sucks - nothing works, it's all linkrotted away."

linkrot by tgjerusalem December 16, 2008