One of the classic ways to build links is through widgets. But with the latest notice posted by Google, it seems that this approach can now be classified as black hat, if it isn’t accompanied with a nofollow attribute.
According to Wikipedia, a (web) widget is a small application with limited functionality that can be installed and executed within a web page by an end user. There are many examples of widget. One of the popular ones is YouTube, from which we can copy the source code into our web page to be able to display a video, and Twitter, which allows us to embed a particular tweet into a web page a nicely formatted manner.
But YouTube and Twitter are so popular they may not need to use widgets to perform well on link building. Other common applications involve stat counters, currency conversion, loan calculator, affiliate travel booking, WordPress plugins and music player. Recently, the idea of infographics became popular and can also carry link back to the originating website.
Google has issued a gentle reminder to widget makers to ensure links found in the code are nofollowed; otherwise the long arm of Google could detect this apparent violation and subject websites to manual action. Matt Cutts explicitly mentioned “I would recommend putting a nofollow, especially on widgets.”
Removing the nofollow directive means the website complies with Google’s suggestions, and may reap other benefits such as branding or even referral traffic. However, having nofollowed widget link means the link carries no weight in terms of SEO, something many widgets are made for this specific purpose.