suspicious text alteration

[<linux@aleblanc.cotse.net>]

Hi,
   I noticed something very suspicious the other day while using emacs.
   I'm sure I saw a text character on my screen (far from my cursor or
   mouse pointer) change to a different character on it's own. 
   I have noticed this a couple of times before in the past, but
   instantly ignored it assuming it was my imagination.

   Here is a list of possibilities I can think of:

        1) I was hallucinating - it was late, but I did not feel tired,
           and double checked myself. 
        2) Software error - I was using emacs 22.3. and did not have any
           modes running that could do something like that.
        3) Harware error - the machine had been running for a long time,
           but is less than one year old. However there is a minor
           problem - when I alter the screen brightness using the fn key
           the brightness indicator that appears is usually garbage. 
           Sometimes it appears as normal though.
        4) Cosmic rays - I have read that computer memory chips can be
           altered by cosmic ray interference, and that this is not uncommon:
           http://www.newscientist.com/blog/technology/2008/03/do-we-need-cosmic-ray-alerts-for.html       
           http://news.bbc.co.uk/2/hi/technology/7335322.stm
        5) Hacker/Root kit - could someone disrupt my workflow by
           installing a rootkit which subtly alters text? or maybe a
           hacker is doing it directly? I did have an SVN server & SSH
           server connected to the internet, and frequently used instant
           messaging with people I don't know very well.

    Can anyone give me advice? Am I being too paranoid? too relaxed? 
    Has anyone else had the same problem or heard/read about it?

-- 
aleblanc