So basically, quite a few problems have occurred over a short space of time when no problems existed before. In the last few days my Microsoft Security Essentials has, every so often, turned itself off. I have managed to do a full scan without it doing this, and it detected one item which I then removed. However, the next day it did exactly the same thing again. In addition to this, my computer has once blue-screened and this seems to be connected with the antivirus problem due to them both happening recently when previously there have been no problems whatsoever. Other (maybe linked problems) are 1) my computer has slowed down significantly (programs open slower, the internet takes a long time to connect after boot up etc.) and 2) My Google Chrome crashes for no apparent reason and shows the 'Aw snap' screen. According to Google, a reason for this can be malware.