Denial Of Service (DOS):
Denial of service is a very ancient type of attack, in which a web server is hanged up because of sending overwhelming number of requests. DOS attack has a sibling also called DDOS (distributed denial of service) in which the attacker simultaneously launches a dozen of requests to a number of servers until they are hanged up.
- Keep a data backup and place them at a safer place.
- Install tools that can test the capacity of your web server against the DOS or DDOS attacks.