Google just announced a big Penguin update (first one in two years) and that these penalties from spammy backlinks will now happen in real time.
More information here ... What is Penguin?
Penguin is the name of Google's penalty for spammy backlinks.
If you have spammed, irrelevant links to your site then your pages can be penalized.
Why Should I Care? I Don't Spam Backlinks
Spammed backlinks are often created by blackhatters...