It could be your ISP pinging you pc to check your online status,it also maybe a networked pc if you on a network,there can be lots of reasons for this alert,can you stop the alerts from showing,then let Norton do its job silently.
Best phone camera 2017
Stunning new film posters by Hattie Stewart, Joe Cruz & more
iPad Pro 10.5in (2017) review
28 astuces pour profiter au mieux de votre iPhone