Why is Nayatel hijacking web page ad requests?

I noticed since the last of couple of days that going to many sites (e.g. news.bbc.co.uk, etc) from a Nayatel connection now brings up Nayatel ads. I'm not sure how ethical what they're doing is, but seeing the same crappy Nayatel ad on a page three times is extremely annoying. Hopefully preparing their network to send spam wasn't the reason they had the recent 12 hour downtime in which they supposedly were improving their network (though I'm beginning to suspect that now).

Of course anyone with a Nayatel connection on a VPN network (i.e. offices) won't get this stuff but regular users do.

I get nayatel ads, then again I get pizza hut ads for pakistan as well and other local ads as well.. its nothing to do with "hijacking" as you call it, pakistani companies pay for advertisements targeted to IP addresses in Pakistan, this way you see relevant advertisements.. What use is being in Pakistan and seeing an advertisement for a british ISP you will never use.

That is not what I meant. Nayatel is not paying anyone for anything. They are replacing the ads shown on the page (whether it's wired.com or BBC or even some Pakistani site which already has local ads) with their own ads. It doesn't matter if the original ad was paid for by some other Pakistani company or British company or whatever. Yes you are right they are not 'hijacking' but they are still silently redirecting requests to ad servers to their own servers and replacing the ads. This is nothing like Google's targeted ads or what you mention. Like I said this is only for people on the Nayatel network. If I open the same page through some other ISP I get the real ads. Note that I don't like ads of any kind and I usually use ad blocker add ons with Firefox but this is just something I noticed. Also Nayatel trying to 'intercept' the ad server requests and giving Nayatel ads only to users already on the Nayatel network is pretty useless.

I haven't tried it, but if I probably use some other DNS rather than Nayatel's then this won't happen (unless they are actually redirecting the IP address).

What is the site link where you are facing this issue?

It was everywhere before (e.g. www.wired.com, news.bbc.co.uk), basically any site that has ads but they seemed to have removed it now. I don't see it anymore.