What is mac-system-alert.com and how do I get rid of it?

It's a scam. They're hoping you'll call the number so they can fleece you for hundreds of dollars for problems you don't have. Either of these will work.

1) Open your web browser's preferences and turn off JavaScript. Back out of the page, or close the tab. Turn JavaScript back on. If you backed out of the page, just don't go forward again or you'll be locked into the same JavaScript loop.

2) Quit Safari. Hold down the Shift key and launch Safari. That tells it not to reload any web sites that were previously open.

Yer' welcome. 🙂

Unfortunately, the purveyors of this annoying crap have updated it. These steps no longer work. HELP!

Yes, some are persistent. Instead, disconnect from the Internet, then close the tab or click the back button. With no way to communicate with the remote server, the page can't stop you from backing out. Then turn your wifi back on, or reconnect the Ethernet cable.

Thanks Kurt, I did that but it still came up and blocked access to the Safari settings. I can only assume that they've "improved" it since Nov-14!

You still need to hold the shift key when relaunching Safari with Internet access disabled. Otherwise, Safari will still reload the cached data on your drive.

I did.

Just tried again, NO change.

That shouldn't be possible, but try this.

Close down, or force quit Safari. Open the ~/Library/Caches/com.apple.Safari/ folder in your user account. Empty the subfolder, fsCachedData. Get rid of any other items named cache. Leave the Extensions and com.apple.Safari.SafeBrowsing folder alone.

Try Safari again.

Kurt, unfortunately, even this didn't work. I also installed Sophos and ran that but it STILL pops up as soon as I open Safari.

Are you certain your Internet connection is disabled? If wired, unplug the Ethernet cable. If wifi, open the System Preferences, click the Network icon, Wi-Fi at the left, and then the button Turn Wi-Fi Off at the right.

Try again. Also, while Safari is up with Internet access disabled, press Command+Option+E. Click OK to clear all cache data. Shut down Safari and launch it again.

Kurt, unfortunately, even this didn't work. I also installed Sophos and ran that but it STILL pops up as soon as I open Safari.

I think we're going about this wrong. I've been presuming you've been fighting a scam page that locks the browser. What I now think you have is adware installed. No AV software will remove adware as it's not considered a threat. It's just really annoying.

You can either follow Apple's manual instructions for removing adware, or use the free automated tool, AdwareMedic.

That's EXACTLY what it was! I left the PC world 2.5 years ago to escape it and it's finally tracked me down. I can't thank you enough for all of you help! And AdwareMedic nailed and removed it on the 1st attempt. It was identified as ~/Library/Safari/Extensions/searchme.safariextz and deleted and, for the record, it didn't interfere with Mozilla Firefox for Mac. I used/use Malwarebytes on the Windoze side and it's excellent but they don't offer a Mac version however, I'm very impressed by AdwareMedic.

Thanks again Kurt!!!