Which of the following is a computer worm that caused a denial of service on some Internet hosts and dramatically slowed down general Internet traffic?

Klez was a mass-mailing email worm known for spoofing sender addresses and disabling antivirus software, not for causing broad Internet slowdowns via network flooding.

Code Red was a worm targeting IIS web servers that defaced websites and launched DDoS attacks against specific IP addresses, but did not cause the same scale of global Internet slowdown as SQL Slammer.

SQL Slammer was a 376-byte worm that fit entirely in a single UDP packet, allowing it to spread at extraordinary speed by exploiting CVE-2002-0649 in Microsoft SQL Server 2000. Within 10 minutes of release it had infected most vulnerable hosts globally, doubling every 8.5 seconds, and consumed enough bandwidth to cause significant packet loss and denial of service across large portions of the Internet.

Beast is a Windows-based Remote Access Trojan (RAT) used for remote control of victim machines, not a self-propagating worm designed to flood network infrastructure.