We have several pc's where I work and employees having to download several pics daily with several different kinds of cameras. Recently the pcs are freezing during the transfer of pics. Do you have any clue as to what would cause this sudden occurance??
I don't know what could be causing the freezing, but I assume they are transferring pics by connecting the camera to the PC? If that's so, I suggest you ask them to try using a card-reader instead, they don't require any third-party software or drivers to be installed.
If this is a recent occurrence and is happening on multiple computers I would suspect some sort of infection. Run scans. You could also try restoring one of the computers back to a time prior to this problem, to see if that corrects the issue.