See this removal guide:
http://malwaretips.com/blogs/fbi-cybercrime-division-virus-removal/As for why it wasn't stopped -- this is unfortunately a common issue these days. It was either allowed by you (unknowingly) or it took advantage of an unpatched exploit with some installed program on the PC -- most likely Java or Adobe Flash.
Unfortunately, these type of malware attacks are difficult to keep up with because they trick you into letting them install. They usually come from an infected web site, and usually through an advertisement. You get a pop-up from the infection and you click it to close the pop-up - which allows the infection to install. They can also be delivered in a "drive-by" fashion with no action needed by the user due to the system being unpatched, no matter what security software is running.
When you encounter one of these fake virus pop-ups while browsing, immediately do the following:
-Do not touch any browser window to close it or browse further.
-Use the key combination <ALT>+<F4> to close all running programs, especially the web browser
--or--
-Immediately press Ctrl-Alt-Del and bring up Task Manager and forcibly end all instances of iexplore.exe, if using Internet Explorer, or the executable for your browser for any other web browser.
--or--
-Go to Start/Shut Down and restart the PC without touching any browser windows.
-If you used task manager to close browser instances, reboot the machine.
-Then go to Control Panel/Internet Options and delete all temporary Internet Files and cookies. If you are using an alternate web browser, open the browser settings to do the same - delete the local cached files and cookies.
-Perform a full scan with MSE.
The above steps should prevent the infection from taking hold.
Start here -
https://support.microsoftsecurityessentials.com/and select the link that says - I think my computer is infected. Options will vary by region, but phone support leads you to Microsoft Answer Desk (
http://www.answerdesk.com/) in the US at this time. After an initial free consultation, a fee will be charged for assistance, based on the details of the case.
This web site -
http://www.bleepingcomputer.com - contains details for many of these common infections, often immediately after they began to appear in the wild, and instructions are provided for how to remove the infections using their malware removal guides. They also have forums where you can seek help from people who specialize in malware removal.
Besides MSE, the following recommendations will assist in protecting the PC from infection:
-Make sure that the Windows Firewall is enabled.
-Make sure that all important/critical updates, including service packs for the operating system and programs are installed from Microsoft Update (Windows Update).
-Make sure Internet Explorer is at the latest version for your operating system and updated with all patches.
-In Internet Explorer 8, 9, or 10, use the SmartScreen Filter.
-Make sure that IE Internet Security settings are at least set to medium-high (default).
-Enable the pop-up blocker in IE.
-On Vista and Windows 7 make sure that User Account Control (UAC) ON and not running with elevated privileges.
-Make sure that Windows Automatic Updates are set to at least notify, but the preferred setting is to download and install automatically. If you update manually, be sure to update as soon as possible after being notified of available updates.
-Make sure that installed applications, especially Adobe Acrobat, Adobe Flash, and Java are at their latest versions. Many vendors are regularly updating and patching for security holes.
See:
https://blogs.technet.com/b/security/archive/2012/07/19/the-rise-of-the-black-hole-exploit-kit-the-importance-of-keeping-all-software-up-to-date.aspx?Redirected=true -Never click through links from unknown sources and use caution even if they are from a "trusted" source.
-Never open unsolicited email attachments.
-Practice safe web browsing.
-steve
_________________
stephen boots Microsoft MVP 2004 - 2020
"Life's always an adventure with computers!"