If you are in Birmingham, United Kingdom, you might check Yelp to find a good Argentinian-style restaurant. You might even see a review that Ivan Stravensky wrote about his favorite restaurant, and decide to eat there based on his glowing recommendation.

There’s only one problem: the review is fake, much like Ivan himself.

When buying something new or trying out a new service, many of us head online to check what other customers think. In fact, over 80% of adults in the United States occasionally read online customer reviews before buying something for the first time. But only half of those who read reviews think they give an accurate description of the product, according to the Pew Research Center.

That is because online reviews and ratings can be manipulated. I know firsthand just how easy it is to fake credibility online: in 2017, I created a fake Russian named Ivan Stravensky. Clearly, Ivan has never been to the Argentinian restaurant in Birmingham, but that didn’t stop “him” from writing a five-star review for it. One person even found it “useful.”