Source: https://blog.ahrefs.com/bad-links/
There is still no clear statement from Google that links are not essential to a site. One thing’s for sure, Google webmaster made mentioned not to build links with the sole purpose of manipulating page rank to benefit a site. Links that are spammy can give sites a short boost in rankings but highly susceptible in receiving a penalty from Google. On the other hand, sites that build natural links aka “link earning” might see slower gains but would have a long term good effect in the long run. Backlinks are still important to Google and will remain a signal that can influence a site’s ranking position.
Manual Penalty – this is given to a site whose link profile was reviewed by Google webspam team and discovered unnatural link patterns.
Algorithmic spam penalty – these penalties are triggered when the Penguin algorithm is rolled out. A good way to see if your site was affected is by looking at your analytics if your traffic has dropped significantly.
Link building tactics that you need to avoid
1. Spun articles – this is done by rewriting articles and posting it to low quality blog and spam sites to increase backlinks. A black hat technique like this should really be avoided since it pollutes your link profile and search engine index by adding similar close-to-duplicate low quality content.
2. Drop comments – or comment spam is a black hat technique by posting comments with no value to blog sites.
3. Low quality directories – this technique has not worked and will never work as long as low quality directories exist and continued to be used as a quick alternative in gaining back links.
4. Links from foreign language sites – if your site is US based or you don’t have cater to international clients then it’s unusual to find a lot of links coming from foreign language sites.
5. Reciprocal links from non-relevant sites – asking for exchange links or link swapping is considered unnatural and can penalize your site as well.