If you transfer a file between two wireless hosts, what kind of speeds do you see? If you have Airport Utility 5.x, you can see a list of DHCP clients. It allows you to more easily spot devices that aren't normally connected to your network.Also if you option click the wifi icon in the menu bar, you should see link speed - do you see this drop at the same time the speeds drop? You can also try MAC address filtering to further enhance your networks security, although I personally find it too much of a hassle.The most common cause of what you describe here is a common wireless interference problem.This probability is pretty high if your network loss of performance was closely related with the move of wirelessly connected computer or of pieces of furniture made of metal or glass (these cause many radiofrequency reflections).ASIDE: I'm not totally convinced that the form-factor change was an improvement.
They'll have access to the internet, but not your local devices.
I let you imagine the nightmare connection since the i Phone was fully used… In fact this was a 3G phone connection overloaded…and shared.
In urban environment, the third most popular culprit for your kind of trouble is someone who either unwillingly or willingly connected to your wireless network.
I first suspected my ISP, but that doesn't seem to be the problem - my speeds seem to be fine through my wired devices (albeit subjectively - I haven't measured), just not the ones connected via Wi-Fi.
My setup is: The devices that are wired (Apple TV, Amazon Fire TV, Xbox One) all seem to perform fine - I can stream video, download game updates, etc. My Macbook Pro, Android phone, i Pod and i Pad are all affected by the slowness, though.