How do I disable Javascript?

There is no need to disable JavaScript. Many websites, including this one, won't work without it.

Read "Ransomware" web pages, part of which is excerpted here.

The "FBI Moneypak" or "lock screen" or "Reveton" or "Mandiant" variants is a popup that refuses to be dismissed, effectively hijacking your browser and preventing you from doing anything with it until you quit the program. It's nothing more than a lame phishing scam that attempts to deceive you into providing personal information such as credit card numbers. If you did not do that, there is no reason for concern. There are countess variants of the same scam with similarly pathetic attempts at impersonating law enforcement organizations from the Bundespolizei to the KGB.

Getting rid of it is simple:

1. Force quit Safari by holding these three keys simultaneously: option command escape

When the following window appears choose Safari and then click the Force Quit button:

2. Acknowledge the following dialog with the Force Quit button again:

3. Then, hold a shift key while you launch Safari from the Dock or from your Applications folder.

This will launch Safari with your chosen "homepage" that can be set in Safari > Preferences > General:

If you were to launch Safari again without holding the Shift key, the previously loaded pages will load again (if you configured that option in System Preferences) and just re-load the problematic code that caused the bogus FBI ransomware to reappear. If that occurs simply force-quit Safari again.

Moneypak itself is legitimate: https://www.moneypak.com/ProtectYourMoney.aspx#

FBI statement: http://www.fbi.gov/news/stories/2012/august/new-internet-scam

Read about the threat and its variants here:

http://www.microsoft.com/security/portal/threat/encyclopedia/entry.aspx?Name=Tro jan%3aWin32%2fReveton#tab_2

Though this scam has allegedly been associated with viruses that attack Windows systems, your Mac cannot be affected by them. Force-quit Safari and forget about it.

JavaScript is always part of the browser. You can't enable or disable outside of the browser. Open Safari's preferences and click on the Security tab. Uncheck JavaScript.

Though I'm not why you would want to turn it off. Much of the web doesn't even work correctly if it's disabled. Did you mean Java, rather than JavaScript? Despite the very similar names, they have nothing to do with each other.

All such ransomware web sites aren't any kind of Trojan or virus since neither actually installs anything on your computer. They are all browser tricks that simply lock you to a web page and do their best to keep you from backing out of, or closing the page. They do that with a common JavaScript command to "do xxx on exit". So when you exit a page, the last command is to do whatever JavaScript is told to do. In this case, it's to load the same page. Your really did click the back button and backed out of the page, but the exit command loads the same page so it doesn't look like you got anywhere.

Earlier versions of these scam pages were easily defeated by turning off JavaScript to kill the loop. Most newer versions block your access to the preferences to stop you from turning off JavaScript. However, it's still easily defeated because what these crooks can't do is stop you from killing Safari itself. So do this:

Press Command+Option+Esc. Select Safari and click Force Quit. Close the panel. Now hold down the Shift key and relaunch Safari. That tells it not to reload any web sites from the previous session.

Isn't Reveton a Windows Trojani:malware?