Yahoo has the honor of being the target of the most significant corporate data breach in history. In 2016, the company disclosed that more than 3 billion user accounts were compromised due to Russian hacking. Using a backdoor, the hackers stole all types of customer information. A lawsuit determined that Yahoo failed to notify its users of the hack, which led to 41 class action lawsuits and a 35 million dollar fine. It also caused the company's valuation to drop when sold to Verizon.