I have an iMac and my ISP is BT Total Broadband (UK). It's advertised as 8Mb top speed but as we're a couple of miles from the exchange, we average around 3.5 to 4. I think I understand the various other factors that affect speed, including things slowing down between say, half six and half ten, when most people are home for the evening. I don't really notice that here, however, I do get a pretty big drop after half ten in the evening, going from the aforementioned 3.5 to 4, down to 0.5, if I'm lucky. Given all other factors are the same as earlier in the evening, any suggestions as to what might be causing the drop?

I used to work beside someone who lived in a block of flats. Someone else in the block had an unsecured connection, so the person I worked with, would hook into their wifi in the late evening, after the person had gone to bed, leave it downloading overnight, then switch off in the morning. Not something I would personally do, but I did wonder if something like that might cause my speed drop? My connection is wpa encrypted, but I understand it isn't impossible to break. Is there a way to tell?

Any help or advice gratefully received.