It's a security risk, some sites relying on this will be affected by malicious content on sites they link to, so at the very least they'll now have to add one o

It's a security risk, some sites relying on this will be affected by malicious content on sites they link to, so at the very least they'll now have to add one of the 2 limiting rel attributes on links that do not require the misbehavior to function. Thanks to the bright and sensible handful of people who add extra cruft to HTML after a brief exchange on a mailing list 3 years after a problem was reported, the other 99.9% of the websites will have to be modified too.