If you use the
internet you know how much damage someone can do to you with just an
image, and that's just visual meme injection - mental malware
a whole new world of sabotage. Viruses propagate because of exploits
in existing system - every copy of a program by definition suffers the
same flaws, so a single exploit can spread through the entire network.
Every mind is different, however, with even the most basic functions
slightly differently mapped in every head so you don't have the same
rapid-infection risk - but you do have a far more chance of malicious
code interacting in unexpected ways and simply breaking part of your
soul while it's in there, with no way to restore it.
The new neologism is "neurosecurity", an excellent addition to the language (which has only been used in infinity-billion sci-fi stories already). If nothing else, you should be terrified of a cerebral SirCam - imagine a virus pulling a random thought from your head and telling everyone you know.
Brain Hacking http://edition.cnn.com/2009/TECH/07/10/mind.hacking/