Over the last few weeks we have noticed that a lot of people have had their computers hijacked by a real looking program called System Defragmenter, however this is in fact a form of virus/malware which shows fake alerts and tries to scare you into purchasing it.
Luckily BleepingComputer has put together a full removal guide for you, a few tools are needed beforehand, all of which are free, these are Malwarebytes’ Anti-Malware (MBAM) (here) and rKill (here). Also I would suggest downloading CCleaner (here) and if you are a home user AVG Free Edition (here).
If you check out this link and scroll down about halfway to “Automated Removal Instructions” follow the step-by-step instructions, if you have trouble with these steps perhaps start your computer in Safe Mode with networking, you can do this by pressing F8 during boot-up and choosing “Safe Mode with Networking” from the list (more detailed instructions here).
Once in Safe Mode I would firstly install CCleaner and open it, once open click run cleaner and remove unnecessary file build up, once complete follow Bleeping Computer’s instructions, this involves running rKill to stop any dodgy processes from running (right click and run as administrator on Vista/7), installing MBAM, updating to the latest definitions and then running a full system scan, once complete your PC will restart and System Defragmenter should have vanished.
I would then recommend installing AVG Free Edition if you have no antivirus software installed, this should help protect you against future infections.
Did this guide help you get rid of System Defragmenter? if not feel free to ask questions in the comments section.