web site hack

I've come across 2 holiday accommodation web sites that seem to be compromised by gaming equipment ads.
To see this, Google on 'Malston Mill' and 'Dittiscombe'. Both have the correct link 
in to their sites, but short description is nothing to do with them.  Click on the 
3 dots and you'll see their caches have been taken over by the advert.

Does anyone know how this exploit works and if Norton can help? 
How do you get rid of this?

Duckduckgo and Mojeek don't seem to have the same problem.

Keith Lockstone