tracking cookie yieldmanager not detected by Norton but resolved

I did several quick scan and the detailed result saying my computer had 4 low risk tracking cookies. 3 of them are not detected (tom@content.yieldmanager.com; tom@ad.yieldmanager.com; and tom@fastclick.net) , the other one is orphan cleanup removed.

However, I have green light "all detected security risks have been resolved" ...or fully resolved even the tracking cookie is not detected ?

My question is this normal ? Should I be concerned ? How can I remove yieldmanager.com, I have firefox browser and manually block the site but after a quick scan, the result is the same.

Please advise

Tom