3. Yahoo Breach

In September, Yahoo confirmed reports of a breach that affected 500 million of its users, the largest number of users impacted by a single data breach to date. Yahoo said at the time it believed the hack was carried out by a state-sponsored actor. The data breach, which occurred in late 2014, has exposed certain user account information, which could include names, email addresses, telephone numbers, birthdays, hashed passwords, and in some cases, encrypted or unencrypted security questions and answers. The company added that it doesn't believe that payment card data and bank account information was among the stolen data. The timing for Yahoo was less than ideal, coming shortly after the announcement that Verizon intended to acquire the company for $4.83 billion. It is not yet clear whether the data breach will affect the acquisition or the acquisition price.