|1.||denial of service|
"Denial of Service" is a type of attack against computer systems that makes a server become unresponsive to any user requests. This is most commonly performed by flooding the server with huge amounts of senseless requests so that the server gets busy computing all those requests.
Normally, a denial of service attack does not compromise the server's security.
The "Anonymous" Hacker group recently started a denial of service attack on paypal so that no one was able to buy stuff via paypal for hours.