I've seen people claim on the web that emails aparently from them have been faked.
Yes, sounds reasonable. In fact, I've had emails faked to look like they are from me and we've recently seen one made to look like it was from silentlambs.
However, as with any claims on any subject, there will be those who make the claims for other reasons. While some people will have been spoofed there will always be a few who haven't and just see it as a convenient explanation or 'get out clause' to dismiss some poor behaviour on their part, usually after they have been found out.
I've even seen cases where people claim that emails from them are faked or the result of a virus but contain replies to emails sent to them or even comments about telephone calls with them !
Do people really believe that their desktop computer, never-mind a little virus, is that powerful?! If it were true then they should pack the whole thing up and sent it to some MIT research institute where the new found miracle of machine intelligence can be examined. Fancy ... after all the efforts by clever researchers, a virus beats the turing test
Just remember - if I ever post anything bad about anyone ... it wasn't me, it was the virus.