There is malware making the rounds right now veiled as a Facebook video, but hijacks web browsers and Facebook accounts
The malware is sent as a link in an email claiming you have been tagged in a Facebook posting. Clicking on the link takes you to a website informing you that you must install a browser plugin to watch the video. The plugin actually provides the perpetrators of this crime the ability to retrieve all stored information in your browser, including saved passwords.
Using stolen credentials from your browser the malware also send messages to your friends on Facebook enticing them into the same scenario. This is allowing the malware to spread rapidly.
Part of the insidious nature of this malware is to block access to the browser settings that would allow you to remove it, as well as block sites that have virus removal software.
Remember to never click on a link, or open an attachment, from any source you can not verify. For more about being safe online read my book.