rel="nofollow" is something every web developer or webmaster should know — because it’s very important for a site’s SEO. When some links are added by users and might be spam links or can’t be controlled, it’s better to add an attribute to these links: rel="nofollow" tells the search engine spider not to crawl that link, so the spider won’t crawl it. “Nofollow” gives webmasters a way to tell search engines “don’t follow links on this page” or “don’t follow this specific link.” Initially, the nofollow attribute appeared in page-level meta tags, used to instruct search engines not to follow (i.e. crawl) any outbound links on the page. For example: <meta name="robots" content="nofollow" /> Now it’s also allowed in a single a tag, for example: <a href="#" rel="nofollow">Renfei</a> What kind of pages should forbid spiders from crawling? 1. Untrustworthy content: If you can’t or don’t want to vouch for the content of the web pages your site links to — for example, untrustworthy user comments or guestbook entries — you shouldn’t follow these links. 2. Paid links: Because paid links may be billed by counting visits, to avoid billing disputes from non-browser traffic, try to also forbid spiders from crawling them. 3. Login/Register: Because spiders prefer valuable pages, and login and register pages often have no valuable information. Finally, webmasters are also reminded: when exchanging links, be sure to check whether the other party’s links have the rel="nofollow" attribute. Normally it should not be marked rel="nofollow"; if it is, you should ask the other party to remove it, otherwise this link has no value and won’t get an effective backlink. Alright, now when you encounter spam links posted by users, you only need to add the rel="nofollow" attribute — it won’t affect user clicks, nor affect the quality of this site, and PR won’t be passed out. If you use WordPress, don’t worry — by default, user usernames and user comment links both carry the rel="nofollow" attribute, so you don’t need to worry about your PR leaking away.
