Hello. I just started using my iMac today, and I've already had a pushy intrusion from something called mackeeper. They wouldn't stop texting me and downloading and wanted to charge me. One of the reasons I bought Apple was because we wouldn't get this

Question

I called Apple support and they were very helpful.  Just concerned that my experience on my very first day was mackeeper telling me my computer was at critical levels and I needed protection.....for $90. 
Nearly everyone I talked to asking about Apple products said they'd never experienced any spam/spy/ or intrusion....not sure what you'd call this. 
Should I be concerned?

Answer 1

MacKeeper and similar utilities are just scams that happen to use very aggressive marketing techniques. You may find that visiting certain, generally unscrupulous websites will leave persistent cookies on your system that cause these intrusive advertisements to appear more often than otherwise. Your best defense is to ignore them, don't visit unscrupulous websites, and set Safari's Preferences to block cookies and other website data "from third parties and advertisers". Find that setting in the Security pane.
While you're there click the button "Remove All Website Data...". That will remove all cookies already present and should stop the popups. You will need to sign in again to any website for which signing in is required. If you don't want to remove all cookies then click Details... and remove only zeobit.com. For all I know MacKeeper may use others that are more obscurely named.
Also, consider blocking pop-up windows in the Privacy pane. They are commonly used for advertisements you probably don't want. If you ever encounter a popup indicating it detected registry errors, that your Mac is infected with some ick, or that you won some prize, it is 100% fraudulent. Ignore it.