Looks like most anti-virus software will not handle the Adware, Malware or plishing sites, (https://www.apple.com/legal/more-resourc...) that lock up browsers. To rectify this issue if it has you locked up, first force quit the app, (option-command escape). Next restart it and hold down the shift key. Do not go back to the infected site.
Avoid installing any thing that purports to "Fix your Mac". Clean my Mac, MacKeeper, MacDefender, MacProtector, MacSecurity, Genio are ones to stay away from. Do not follow any links to "Repair your Mac". Always check a phone number before calling by doing a search for Scam & that number or link. BE Paranoid! MicroSoft is not calling you! https://www.microsoft.com/security/onlin...
The way this scam works is that a hacker takes over a legitimate website, and this directs you to a a fake website that pretends to scan your Mac and find malicious software. It then convinces you to download the program to check for the malware, and enter your Apple ID and password to install the program: this program itself is the malware.
Over time it will pretend to scan your Mac, pretend to find problems, and try to get you to enter your credit-card details to fix the problems. If you enter your credit card details they are passed on to scammers who try to get money from your account.
What to do when a website says you have malicious software on Mac? If you are browsing a website and it claims to have detected malicious software, malware, or a virus (or simply states it has "detected problems" with your Mac), then follow these steps:
If you're in Safari (or another web browser) and get a warning about malicious software, virus, or problems detected, quit Safari by choosing Safari > Quit. If Safari refuses to quit, force-quit the app (Control-click the Safari icon and choose Force Quit).
Go to the Downloads folder and drag any install files, or files that you don't recognise, to the Trash.
Empty the Trash (Control-Click the Trash icon and choose Empty Trash). By doing this you will dodge the problem in the first place. You haven't installed any software, or handed over your credit-card details. I'd suggest you don't return to that website.
How to remove Mac malware (for free): How to protect your Mac from malware in the future
Now that you've checked and removed any malware from your Mac, you may want to ensure that your Mac doesn't get any malicious software in the future.
Here are some tips to follow to ensure you don't get any more malware:
Ensure your Mac is up to date. Open the App Store app and click Update All.
Turn on automatic updates. Open System Preferences and click App Store and select the option Automatically Check for Updates. Make sure both Install OS X Updates and Install System Data Files and Security Updates are also both selected.
Make sure the Mac only allows apps from trusted developers. Click on System Preferences > Security and Privacy and General. Check that the option under Allow Apps Download From is set to either Mac App Store or Mac App Store and Identified Developers. If it is set to Anywhere, then click on the Lock icon, enter your password, and change it to either Mac App Store or Mac App Store and Identified Developers.
Get your software from the Mac App Store or from developers you know and trust.
Here's the best of anti-virus software: http://www.macworld.co.uk/feature/mac-so...
Get to know the enemy and their tactics: http://malwaretips.com/blogs/remove-tech...
Tom Reed puts out a good guide: http://www.reedcorner.net/mmg/