The HTML widget is basically an iframe.
But some sites will not allow you to show their website from another domain, especially those that allow user input. For an example, lets say you put Facebook on your domain, and you sized the iframe 50% while the other 50% is your site looking like Facebook. A user inputs info they think is going to Facebook, but is actually being caught by your site, perhaps credit card details, email addresses etc. So it is 'forbidden'
Best thing you can do is take a screen shot every day, or even use a library and clone, but they not very good, and use that.