Worms - look for vulnerable computers across network to copy itself. Unlike viruses, worms do not need to parasitically attach to other programs, but NEED NETWORK TO SPREAD.
Worm is a good vehicle to carry Malware.
Find target IP address to infect; compromise target by an exploit or social engineering; t/f copy of worm to target by email or ftp; can contain payload e.g. Trojan Horse, virus, DoS agent. backdoor or remote access Trojan (RAT), bot to join Botnet, SMTP spam relay server.
Code Red was a targeted DoS to whitehouse.gov
SQL Slammer only 376 bytes, buffer overflow exploit compromised vulnerable MS SQL Server 2000 machines (but had no payload, but just spread itself), uses UDP - connectionless and is fast.