My linux desktops keep complaining that they're being port scanned amongst other things. Turns out it's coming from a windows PC on my network. I'm pretty sure the windows PC is clean, but hey, not 110%.
IS there any reason for this activity from a windows PC, other than it's got a virus?
Does your linux system tell you which ports are scanned? Windows is quite active in finding other Windows computers on the net and your linux box might just be triggered by one of those requests. A list of all ports which Windows systems use in their communication can be found here [support.microsoft.com]. If linux reports other ports, you have a hidden port scanner on your Windows computer.
Another thing you can do is to open a DOS prompt on your windows box (In Administrative mode if it is a new windows version) and type the command netstat -anb. This will give you the names of all processes which are currently involved in network activity, including the IP addresses and ports they are using.