I'm not sure if it still works like this or not, but up here in Canada with Shaw cable for the longest time, it just started out of nowhere one day, I'd always get redirected to a Shaw landing page or have Shaw ads injected into pages when I was browsing. I finally really noticed it one day so I did some searching at the time and found out Shaw has an option in their account page(enabled by default),

I can't remember what it's called, something like 'Shaw enhanced browsing' or some shit, but basically this 'feature' allows shaw to route traffic through their servers and inject content into sites. There was no description of this option in the account settings, they were buried 3 or 4 layers deep, there was no mention of this 'feature' from any of Shaw's customer service people, the only way I discovered this was through some random forum conversation I found.

There was also people mentioning (this never happened to me)that despite switching the option off, they would find it turned back on again a day or two later and have to repeat the process. I have no idea if this is still the case, this would have been quite a while ago now, but I was pretty unimpressed when I figured it out and realized what was going on.