That is MALWARE.... a fake... you going to have to go on internet to find how to get rid of it on the Mac or take to computer shop to fix it.

No, don't listen to WestEnd. You can easily remove this with malwarebytes. Simply go to malwarebytes.org, install it (It's free and trusted) and run a full scan. That should remove this virus.

I agree with '''Tyler Downer'''

The [https://prod-cdn.sumo.mozilla.net/uploads/images/2018-06-13-07-49-57-2a6cce.png screenshot you attached above] shows that the problem pop-up is titled '''Advanced Mac Cleaner'''. Here are links to discussions I found on Apple's forum avout this malware, in case it helps: ----- Q: How can I get rid of Advanced Mac Cleaner (Document Type: Discussions) Apr 7, 2018 How can I get rid the Advanced Mac Cleaner that has popped up on my computer https://discussions.apple.com/thread/8334195?language=en Q: How do you uninstall Advanced Mac Cleaner? (Document Type: Discussions) Apr 13, 2018 Another option. Advanced Mac Cleaner uninstall (2) https://discussions.apple.com/thread/8301869?language=en Q: How to Remove Advanced Mac Cleaner Virus (Document Type: Discussions) Apr 24, 2018 I have just noticed on My Macbook Air that window pop up on my Macbook Air apps Advanced Mac Cleaner and inform... https://discussions.apple.com/thread/7245101?language=en Q: Blocking a Site: Mac Cleaner (Document Type: Discussions) Mar 29, 2018 and a message that MacCleaner had found 503 errors on my computer and a virus. I have seen things from Mac Cleaner before... https://discussions.apple.com/thread/8334915?language=en ----- Also, the [[Troubleshoot Firefox issues caused by malware]] article has more information, including a [[Troubleshoot Firefox issues caused by malware #w_mac-security-and-malware-protection|Mac security and malware protection]] section for Firefox uses on macOS.