Update Alerts

My computer is showing a notice via an update alert that a new update is available.
When I click “Yes” to load it down no file appears and the update does not show in spite of the fact that you can hear the hard drive receiving file information.
WEhen I run my safeguads such as Webroot and Norton it show I have infected files.

My question(s) are
1(a) how do I ensure this update is genuine?? None of the programs I can physically check say thet they require them.
1(b) how do I remove this update notice if it is not genuine??

Many thanks,

Doug