I'm a bit unclear as to the problem... are you seeing ads where there should not normally be ads? If so, you may have adware installed on your Mac, or you may be on a compromised network. See my Adware Removal Guide for help identifying and fixing such problems.
As for Symantec, note that all Symantec products are bad news on the Mac. They cause all manner of problems and their ability to detect Mac malware ranges from just so-so to abysmal, depending on the product. Any Symantec product should be uninstalled immediately, and you should read my Mac Malware Guide for information on how to properly protect yourself against malware.
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