On February 7, 2000, and continuing in the following days, six of the most popular sites on the World Wide Web were brought to a stand-still by a concerted effort of computer hackers. The attack started with Yahoo! on Monday. Buy.com, Ebay, CNN.com, and Amazon.com were hit on Tuesday, and ZDNet reported that it was the latest victim of the hackers on Wednesday morning. Each of the sites has suffered from what is called a "Denial of Service" (DoS) attack. In a DoS hack, the hacker does not need to gain access to the computer server; instead hackers send a huge volume of fake traffic, which blocks actual users from accessing the site. Yahoo!, for example, was hit with 800 megabytes of data per second, "more than 24 times the normal flow of data." Each of the sites was unable to be accessed by users for several hours. Buy.com was an unfortunate victim on the day of its IPO. It was, however, able to recover, closing that day at 25-1/8, though it peaked earlier that day at 35-7/16. Although the FBI has been brought in to investigate, this type of attack is very difficult to trace.