GIMP is available for windows. Linux is suseptible to viruses, but the hackers typically don't spend time making viruses for lesser used operating systems. Most viruses are -made- specifically to attack a windows or mac computer. Windows is idiot proof if you have a little bit of computer knowledge.
The colouring is nice, but it still needs a little bit of work. Perhaps a little more colour detail and depth, you can even try using different brushes to add effects to Wynaut's body.