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OK.  There's no known Penguin update that happened in January.  Although links are a possibility, there could be something else.  Panda is certainly a possibility and also it's possible that there is some sort of technical issue that is affecting the site. It sounds like you probably need someone with knowledge of Google penalty and algo changes to have a good look at the site and dig into your analytics.  I am not personally able to take on new audit work right now but I can put you in touch with someone whom I know is good at this kind of stuff.  You can find my contact info via my profile. There are also some very knowledgable people here in the Moz forums that would probably be available for hire for an hour or two to have a good look.  You can search for similar questions and find people who have good reputation and have given good answers and pm them to ask for consulting.