Hijacked Web Traffic For Sale
mask.of.sanity writes "If you can't create valuable content to attract users to your site, Russian cyber criminals will sell them to you. A web store has been discovered that sells hacked traffic that has been redirected from legitimate sites. Sellers inject hidden iframes into popular web sites and redirect the traffic to a nominated domain. Buyers purchase the traffic from the store to direct to their sites and the sellers get paid."
Isn't this what websites do all the time with ads, and Facebook and Google+ buttons? It's not like I personally agree to send my traffic to Facebook when the button shows up on a random webpage, and visiting all those ad servers incidentally just slows down my web browsing for no good reason.
You are correct. AJAX cannot be cross-domain.
There is however a catch, since a lots of libraries will allow you do do cross-domain "AJAX-like" request by adding a "SCRIPT" object to the page dynamically. You can't POST but you can GET fine with this method since the SCRIPT tag is cross domain.
Write boring code, not shiny code!
https://en.wikipedia.org/wiki/JSONP
https://en.wikipedia.org/wiki/Cross-Origin_Resource_Sharing
The iframe loads in a line of javascript which initiates a redirect to the target site. The user doesn't need to click on anything as the javascript will run automatically.
What this means in practice is that as soon as a user loads the page they will be redirected to the target site, probably so quickly that they don't realise. This is what makes it so dangerous as the user can be redirected to a page that is almost identical to the genuine one and then convinced to login to the site giving up their login or bank details etc.