(24/7 News)  --  A Boston University study says one out of every five reviews on Yelp is fake. 

The study analyzed more than 315,000 of the site's reviews and found the rate of fraudulent ratings went from five-percent in 2006 to 20-percent today. 

Researchers suggest users be skeptical of both five- and one-star reviews.  Four-star ratings showed the highest rate of legitimacy.