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In Magento Admin new secret key is generated every time you login. It is a unique key 32 Characters long for each session of your Magento admin login. This key is appended to the admin URL as http://test_admin/key/78c1c0a77f2336c0b2dec9ac934af968/ this is only for the security reason.
In Magento release note, it is stated that they have added secret key to URL for CSRF (Cross-site request forgery) Attack Prevention, for CSRF Please read here http://en.wikipedia.org/wiki/Cross-site_request_forgery
If you want to remove/disable the Secret key from the Url, follow the give Steps:
Step 1 : Login to admin Panel
Step 2 : Go to System -> Configuration -> ADVANCED(Left Bottom) -> Admin -> Security -> Add Secret Key to URLs Refer Screenshot
Step 3 : Select No
Step 4 : Save Config
Now check the admin Url there will be no any secret key in it.
