I have TOT modem (Thomsen).Lately,my niece use to come to my home and turn on his computer.My feeling is,that it makes my reception worse,but I am not sure,because many times it is bad anyway.My question:does it matter,how many computers "use" the signal at the same time.My gf sais no,"because in an office,there are many computers"..And yes,I know,I can check by asking him to turn off,but as I said,sometimes it is bad anyway,so it is not conclusive evidence..

Not worse reception but sharing the same band width makes it slower.

^ +1

(Simplified explanation:) If you have a 5Mbps ADSL connection with only your computer connected, theoretically you will get the full 5Mbps speed for use on that computer. If your niece (? you refer to them as "he") is using 3Mbps for a video download, then there is only 2Mbps available for your computer.

Now, a good discussion would be how the ADSL modem/router decides who gets how much bandwidth. (Other than QOS, that is.)

If your router has a "Guest" option, I think you can restrict the bandwidth allocated to the Guest, but I think a Guest account is only on high end modem/routers.

Gonsalviz and wpcoe,thankyou both of you for answers! As a sidenote,when I told my gf about this and asked her to tell the niece,that he is wellcome to use "my" internet any time on any day,exept between 17-21 on saturdays,(when there is a special program from my country on)she was angry and complained,that the niece "will be angry and never come here again".(He is 20 years old).Well,well....