Let's say I have a site like stack overflow. People post comments with - possibly - links to external sites. Is there some "standard" set of rules to make it reasonably safe for users and website?
I have noticed the following features on other websites:
- All links have nofollow attribute, that helps to reduce site penalization by search engines.
- The sites usually made some screening of the target link. Because it usually offers the target page's title for link description at the time of writing the comment.
So, should I always screen the link target's content somehow? And perhaps allow only some mime-types, even then I am not able to guarantee it won't change after some time anyway? Should I disallow link shorteners (like bit.ly), to make it harder to hide actual target link? Should I check the links regularly?
Do You have any experience with this domain?