For those of you who want to take a peak at VirMask.raw, here's a little viewer. It includes the VB source code, and a compiled exe for those without VB. I included VirMask.raw in the zip, so you won't need to extract it from maps.vol yourself.
This file is (probably) used to display both the virus overlay on the map (the purple blight region) and the edge of darkness at nighttime. It shows the tiles along the top, and there is a clickable 4x4 region (well, two actually) where you can select which tiles are light and dark, and it'll display the results.
When determining which tile to display, it examines 4 tiles in a 2x2 setup, using 1 bit from each tile to get a 4 bit index. (There are 16 tiles in VirMask.raw). It's probably easiest to think of the actual virus display as being off by half a tile.
I should note that I cleared the last tile to 0, since it seemed to contain some garbage. When talking to Hacker we figured it was unitialized memory that got saved to the file. That tile doesn't seem to be used in game, but I used it, so I cleared it to 0 to keep the results looking nice.
Edit: Replaced the zip file with a new one. Had a file missing that was stored in a different directory.
