Roger said:
Very unlikely. E-mail travels as ASCII text, and the server would
have to be infected with something capable of decoding
'attachments' - infecting certain types of executable
'attachments' - and re-encoding them before sending them
along.
I don't know how other SMTP software works, but we have some old
software (Post.Office) running our e-mail. It separates the body and
header of incoming e-mail into their own files (in plain text) in each
user's separate directory where they sit until retrieved via pop-3
access. Norton anti-virus (any version works equally well) scans the
whole machine (including these directories) twice daily and frequently
intercepts viruses stored as mime or ASCII attachments and quarantines
them. Recipients end up retrieving blank e-mails (ie no body) in
these cases.
I don't think the issue here is that a virus would decode and
surgically implant malware into an intentional attachment. Most legit
attachments are images of some sort (jpeg usually) and implanting
executable code into a jpeg (and not changing the file's name or
extension) wouldn't seem to have any effect beyond screwing up the
image. Some legit attachments are .pdf, .doc and .xls, and again the
virus would have to have built-in knowledge of what to attach to those
files to render them harmful - and then wait until any such e-mail
(with a legit file attached) passed through the system.
Remember that there have been exploits on web servers where harmful
script was attached to pages served up by infected web farms directing
the browser to malware. It's not hard to imagine that a similar
infection on an SMTP server could result in a viral attachment being
added to every ->legit<- e-mail being sent or received by the server.
Much more effective (for viral distribution) if malware comes attached
to an e-mail coming from someone you know, or are expecting,
especially if the body of the e-mail is part of a legit e-mail dialog.
