Source: http://www.bruceclay.com/blog/seochat-link-building-and-penguin-disavow/
Building links in the penguin age requires attention since it can penalize your site. Keyword and traffic drop during a penguin update could be a sign that your site might have been penalized by the algorithm. This means that your site might have excessive low quality links that Google thinks manipulative. Not only that, asking for links can put your site into penalty according to Google webmaster guidelines.
How hard is link building post Penguin?
A lot of people mentioned that it is hard to build links when comparing what SEOs used to do before penguin. This is because a lot of efforts are invested in looking for opportunity for your site to earn links as well as creating unique content that shareable as a part of link building strategy.
Is link building a black hat technique?
If your intent is to earn links to rank on Google, it is considered black hat. Link earning is the proper term for websites creating unique content to that users would want to link to. Links are a ranking signal and is still a big factor on Google rankings.
Is it ok to ask for links?
As long as links are relevant and you can provide something in exchange other than reciprocal links. It’s acceptable to ask for links as long as it adds value to both parties.
On Disavowing links:
– Use tools such as Moz spam analysis tool, Ahrefs, Majestic to identify weak links that are subject for removal.
– It is recommended to only submit a disavow file if a site encountered a penalty.
– Keep in mind that effort must be done when removing links and using disavow tool is a last resort.