notification hijack

Solution needed. I accidentally clicked on a hijacked 'Notification' as shown by the link picture below.

It keeps reinfecting Safari even after cleaning the cache and disabling javascript. Any ideas on how to stop it from appearing. The first time I accidentally clicked on it, it took me to a porn site, so it probably came by some shareware, etc. It appears every hour and only affects my Safari browser. The Chrome browser on my Mac is not infected. Any ideas? Thanks.