1. Remove Security Tool
Recently, quite a number of staff infected by Security Tool.
This is so called Rogue software.
User simply click some link in the internet, the software will install itself.
What this infection does:
Security Tool, otherwise known as SecurityTool, is a rogue anti-spyware program from the same family as System Security. This program is promoted through the use of Trojans and web pop-ups. When this rogue is promoted via a Trojan it will be installed onto your computer without your permission or knowledge. When promoted via web pop-ups, you will be shown a pop-up when browsing the web that states your computer is infected. If you click on the pop-up you will be brought to a page that shows an advertisement that pretends to be a fake online anti-malware scanner. At the end of the advertisement, it will state that there are infections and then prompt you to download and install Security Tool onto your computer.

3. How to Remove
First of all, you need to download 3 softwares from here :-
1) rkill.com -- end the processes that belong to Security Tool
2) Malwarebytes' Anti-Malware – a high recommened anti-malware software
3) Hostsperm.bat -- SecurityTool changes the permissions of the HOSTS file so you can't edit or delete it. This BAT file is to fix these permissions.

4. Remove Instruction (Summary)
1) Reboot your computer into
Safe Mode with Networking
2) Run rkill.com
3) Launch Malwarebytes' Anti-Malware, update the software and database to the latest
4) Run “Perform Quick Scan”
5) Remove all the listed malware
6) Run hostsperm.bat

9. More Detail Here is the link for the detail :-