You should be safe. There are
viruses for Word docs and other non-executables. Such viruses will attached to say a Word doc then use the MS Word macro/script feature to propagate itself. But, in order for those viruses to be executed, their files have to be opened in their respective programs.
The safest course of action would be do:
- Install a virus scanner on current (possibly infected) PC and virus check files to be backed-up
- Back up files to external storage
- Wipe computer and re-install from scratch
- Install virus scanner on new OS of computer right away
- Scan it
- Scan those backed-up files on external storage
- Restore files from external storage
Yes, that's a pretty paranoid set of steps, but there are a few remote attacks to guard against. Some viruses can install payloads in the hard drives MBR (master boot record) which is typically not over-written by a disk format and OS re-install -- for Windows at least. So, even if you re-install Windows and re-format the drive, the previous MBR will likely remain intact, and if that is infected, then the virus will persist. I believe any decent up-to-date virus scanner will also cover the MBR.
In a similar fashion, there is an outside possibility that your external storage could be infected with a virus as well. If the external storage is a USB drive, then it could be infected in a similar fashion to the MBR. It's not quite the same as you don't boot off the USB drive, but if Windows does the stupid "autorun.exe" type stuff, then a virus could put one
of those files on the external drive and if Windows auto-runs it, then you're screwed. The same logic applies to a CD/DVD.
One option is to FTP your files up to some web site. That way you don't have to worry about a USB drive or DVD/CD getting infected in any way. Sure, your files could still be carrying viruses, but at least the external storage won't be compromised.
If your virus scanning software has a boot disk (such as CD/DVD) where you can boot directly off of it, use it. This way, the virus scanning software can scan the hard drive before anything it run from it. This will help better detect an MBR infection on the hard drive.
Although the most common viruses are attached to executable files, they can certainly also be attached to non-executables. For example, with Word files, viruses are basically Word macros/scripts. They run when Word opens the file and they often infect other Word files. More pernicious are viruses that attach to media files and use attacks such as buffer-overflows to run their executable payload. Such a virus could infect a MPEG, but then install an executable virus in the MBR.
That said, for all but the most compromised systems, you should be fine with: virus scan, backup, re-install, virus scan backup, then restore.