DoS stands for Denial of Service Attack. DDoS, or Distributed Denial of Service attack, is a more complex invasion within the same category.
The purpose of a Denial of Service attack is to make a website or service unavailable for users over the Internet.
To enforce this, the attacker uses bots — a computer that has been invaded by a hacker and is now being used for the attack, to create a virtual army.
DoS and DDoS attacks are dangerous and hard to counter. A DoS or DDoS attack, when properly launched, can render a website or server unavailable for service within a short span of time.
The attacker then deploys a special code on these computers, which starts bombarding the website or server with continuous HTTP or ping requests, resulting in a server overload. Targets are usually high-profile websites, such as banks.
The DDoS attack is very hard to trace due to the high volume of hacked computers being used to infiltrate the system. Owners of the computers used in DDoS attacks are almost always also victims.
To protect your website from a DoS or DDoS attack you must define a standard security policy that specifies the rules of connection and session maintenance for hosts. Set firewalls in place to prevent intrusion.