Google’s Penguin update has rattled many webmasters. Is it still safe to get backlinks from other websites? Can other sites hurt your rankings? What is the backlink profile of your website
Check the backlink profile of your website
The backlink intelligence tools in SEOprofiler make it easy to check the backlink profile of your website. For example, enter the domain of your website in the ‘Get backlinks by competitor‘ tool. You will get a detailed overview of the link types that point to the domain:
Nofollow links are fine
You might have a link on a website that looks like a paid link. If you get visitors through that link, it makes sense to keep the link.
In an online discussion, Google’s John Mueller confirmed that links that use the nofollow attribute don’t have an effect on the rankings of the linked site:

There are some good examples listed in this thread – such as event sponsors, etc.. They aren’t taken into account when we review sites with regard to paid links or other link schemes, nor are they used for things like authorship. […]
If you’re seeing issues with your site with regards to paid links, link schemes, or similarly, then apart from just removing those links, you could add the rel=nofollow instead, especially if you feel that these links have been useful in driving users to your site.”
In other words: if the link to your site uses the nofollow attribute then you don’t have to worry if it is an unnatural link.
Backlinks that Google considers spam
In another online discussion, John Mueller said which backlink types Google doesn’t like:
Focus on things that you can influence
If you did not activiely promote your website with the shady linking methods mentioned above then you probably don’t have to worry about unnatural backlinks.
In that case, it is better to focus on things that you can influence: try to get good backlinks to your website and optimize the content of your web pages.