Security System Warning popup message

It is a scam. They are phishing for your personal information so that they clean out your bank account.

Read Phony "tech support" / "ransomware" popups and web pages.

But should I do anything else to protect against anything?

Those scam messages are a mere inconvenience, like a telemarketer who might ring your phone trying to sell you some garbage. As such, they do not constitute a threat from which any protections are required, or that would be effective anyway. Dismissing the scam message is analogous to hanging up on an unwanted caller.

Has my system been compromised?

Not unless you called the phone number or otherwise performed some action based on the fraudulent information it presented.

Unfortunately did fall for this, and gave remote access for about 30 minutes. We immediately shut down the computer afterwards and realized it was a scam. We took the computer to the Apple store, where they did a scan and deleted installed files and other info by the scammers and was told that we did NOT need to erase the hard drive. I have been since reassured by additional apple support techs that it is not necessary to erase the hard drive, etc. and that I can use my computer. I feel comfortable after hearing that, but after reading things in the apple community, should I be concerned? Do I really need to erase and reinstall the Hard drive?

Do I really need to erase and reinstall the Hard drive?

My recommendation would be to do a complete erase and the install OS X and manually install apps and data using Time Machine using a previous time. I would also contact my bank if any bank or credit card information was provided and follow their advice.

Do I really need to erase and reinstall the Hard drive?

That is a personal decision only you can make. Since I have no way of knowing what the criminals did to your Mac, nor what Apple did in an effort to reverse those changes, would be imprudent of me to recommend otherwise. If I were to take possession of your Mac though — and if it was no longer considered evidence in a potential criminal proceeding — that's what I would do.

Pursuing criminal charges against the scammers is also a personal decision only you can make. These scams can arise from anywhere on Earth, by anyone possessing (or even renting) a telephone and a computer, and are usually beyond the reach of your local law enforcement's authority to act. Among actions worth considering is filing a complaint here: https://www.ic3.gov/default.aspx

Thanks. At this point, I'm considering buying a new computer. As you said, there is no way to know what they accessed on my computer.

That's overkill, but don't let me stop you.

FWIW I agree 100%.

No I know it is! Was not too serious.

i got this message this morning and did call the number. I was put on a brief hold (5 seconds) got suspicious and hung up. i was immediately called back from Viet Nam but did not take the call. Any danger here? I gave no one any information on the brief call except that i got the message on my iPad.

There is no danger from placing the call, unless you divulged personal/financial information, or permitted the criminals to access your computer. For future reference, any such message will always be a scam.

Phony "tech support" / "ransomware" popups and web pages