It depends on how up to date your operating system and application software is on your PC. It also depends on the efficacy of your anti-virus software.
It is possible to have virii (viruses(?)) or malware embedded in image files and video files. Just viewing the image can, with vulnerable software, trigger an infection. My business and government enterprises block jpg and video attachments on emails for just that reason. Essentially the hacker/virus writer sends an "badly formed" image file. A badly written image viewer will crash on attempting to open the image file leaving the way open for the virus to load some exploit code by inheriting the permissions of the viewer process that died. This is why the security people say NOT to routinely use your PC when signed on as an administrator. If you are running a process as an administrator and the process is hacked the exploit inherits administrator rights. Good anti-virus software usually catch this type of attack by not always.
All you will see in such a hack is that the application you are running suddenly fails, meanwhile the malware is busy corrupting taking over your PC.
Make sure you keep up to date with Microsoft Update, check the results to make sure there has been no update patch failure.
I use a free tool from secunia.com to automatically check my software daily to make sure that I have the latest versions.
Now Zen, but a +Net residue.
