Last week, the Federal Trade Commission sued Amazon, alleging that the online retailer was illegally maintaining a monopoly. Much of the FTC’s complaint against Amazon was redacted, but The Wall Street Journal yesterday revealed key details obscured in the complaint regarding a secret algorithm. The FTC alleged that Amazon once used the algorithm to raise prices across the most popular online shopping destinations.

People familiar with the FTC’s allegations in the complaint told the Journal that it all started when Amazon developed an algorithm code-named “Project Nessie.” It allegedly works by manipulating rivals’ weaker pricing algorithms and locking competitors into higher prices. The controversial algorithm was allegedly used for years and helped Amazon to “improve its profits on items across shopping categories” and “led competitors to raise their prices and charge customers more,” the WSJ reported.