You're exposed to "clickjacking". It means that someone can generate a script to completely "destroy" you click stats (including bounce rate, time on site and many other sh*ts that G count on quality sites). Or, they can use your own layout to rank other sites... or... or... or... definitively not good.
If you want to block other sites inserting your own site in their pages using iframes, you could add this to your .htaccess file:
Code:
Header set X-Frame-Options SAMEORIGIN
This block the "iframing" of your site but you can still use iframes on your own properties.
I wouldn't do redirects from "scumbag-site" to my site: the site A maybe compromised/poisoned/penguinized/pandaliez/malwarized and as we all know, 301 redirects pass a lot of good things but also a lot of sh*ts.