Even using the greatest care in the world when opening email, attachments or even clicking on a very benign looking links has inherent dangers. Hackers and malware afficienados have become very sophisticated in their efforts to attack vulnerable computers. Good grief, the OPM just got hacked. the bottom line is to get a thrd party program that updates definitions on a daily basis. Whether it's Security Essentials, Panda, AVG, Bit Defender or any other application, just get it