After a recent definition file update, Norton Anti Virus, Norton Internet Security etc. detect a low-risk adware infection named Adware.Mirar if you have turned on Immunization in Spybot Search & Destroy.
(Immunizations adds a domain used by Mirar to the restricted zones list, and Norton erroneously interprets the presence of the entry).

You shouldn't let Norton "fix" the problem (doing nothing is the recommended action anyway).

See NAV Daily - Calendar Of Updates.