How do I get rid of Zeus24 trojan scam once and for all?

I have multiple times got the fake virus and fake trojan Zeus24 on my Macbook. All it does is pushing out these critical warnings saying my computer is under attack from this virus and trojan. But it all it does is trying to trick me in getting a subscription of McAfee Antivirus. And sadly I did fall for that the first time.

And after I installed that worthless McAfee app it didn't find any virus or trojan. The system still pushed out warnings at an alarmin rate...

I did a little Googling, regretting that I didn't do that in the first place.. Stupid me... And it turns out it actually just a push notice scam and very annoying.

The solution is to empty Safari History and Cache... It goes away.. BUT... It keeps coming back. After a couple of days its back, and pukes out this alerts... I am not poking around any suspicious sites. I don't go to p*rn or torrent sites...

SO.... HOW do I get rid of this once and for all? I am tired of having to empty out cache and History 2 times a week.. All the sites I visit, I have to type in passwords and stuff after I have empty out the cache...

Is it a weakness in Safari alone? Or do Chrome and Firefox users get this as well?