I have seen on several sites that they embed the like button as an iframe not the standard fb-like tag that Facebook recommends. It looks like this:
<iframe src="//www.facebook.com/plugins/like.php?href=PUT_URL_HERE&width&layout=standard&action=like&show_faces=true&share=true&height=80" scrolling="no" frameborder="0" style="border:none; overflow:hidden; height:80px;" allowTransparency="true"></iframe>
Is this practice permitted by Facebook or the owners of the sites risk something ?
Looks like the old embed code with the iframe. Should still work, i guess, but is definitely not recommended to use. Always use the code from the Like Button Plugin page. The iframe solution MAY stop working sooner or later, but it´s definitely not "against the TOS" ;)