Hi,
Over the years there have been new wireless protocols developed. A, B, G, N, and now I think even a newer one is starting...
It may be that your previous devices simply didn't detect this particular protocol..
If your older devices didn't detect N, and the unknown devices are in fact N, that would explain why they weren't there before... This is just a guess because I know nothing about your device specs.
The fact that they are visable doesn't mean "Connected"... I haven't played with any wireless lately so I don't remember what can be made "Not Visable" for instance, but previously when trying out wireless I had numerous "Devices" show up on my list, but
was blocked by their device from connecting to them.
Some weren't blocked though, and I was able to connect through their device...
Maybe you can turn off the capability of using the A, B, G, N, or whatever you are not using...
If you use N and they do too, then that won't work...
Can you select a specific channel for your use that there are no other devices detected on?