Assessing the type of penalty is always the first step for an SEO analysis. When a website receives an algorithm penalty like Penguin, there is no warning except for a loss in SERP rankings and corresponding loss in traffic. More often than not, this penalty can be easily attributed to either a new link building campaign or a major algorithm update that has hit you for existing links.
On the other hand, a manual webspam penalty can be discovered by checking the site’s status on Google webmaster tools so this is always the first step. To check for an unnatural links penalty or unnatural links warning, log into your webmaster tools account, select your site, click on the “Search Traffic” menu to expand it, then click “Manual Actions“. See the red circled menus items on the image below:
Once you reach this page, check if there is any stated penalty under “Sitewide Matches” or “Partial Matches”. If there is anything here it is a manual penalty. In this example case, there is a manual penalty under “Partial matches”. Expanding it, this is the specific message:
Obviously there are many different types of manual penalties. This particular penalty message is usually for a more mild manual penalty. If there is no penalty message here, it is most likely an algorithm penalty. Since this is a common misunderstanding, I’ll repeat this in bold for emphasis:
If there is no manual penalty message, it is probably a link-based algorithm penalty.
What About Panda?
From what I have seen, Panda has been toned down some and/or most people are well aware of it. The good thing about panda is how often it refreshes (supposedly roughly once every two weeks). If you made recent changes in site content or structure in the last few weeks, it may be a Panda (on-site) penalty. But if nothing has changed recently onsite, you can usually rule Panda out. In this case, it is most likely the Penguin (link based) algorithm penalty. Penguin is the most common Google penalty but potentially can be fixed with a disavow alone.
If you have a manual or Penguin penalty, definitely check out our encyclopedia of risky links and link building practices.