CIH, also known as Chernobyl or Spacefiller, is a Microsoft Windows 9x computer virus which first emerged in 1998. Its payload is highly destructive to vulnerable systems, overwriting critical information on infected system drives, and in some cases destroying the system BIOS.
The Anna Kournikova Virus was a worm that spread by email, disguised as an email attachment with the filed name “AnnaKournikova.jpg.vbs.” The virus was a Visual Basic script that, once opened, emailed itself to all the contacts within the user's Outlook address book.
Unlike the Melissa virus, this threat came in the form of a worm -- it was a standalone program capable of replicating itself. It bore the name ILOVEYOU. The ILOVEYOU virus initially traveled the Internet by e-mail, just like the Melissa virus.
Melissa is a fast-spreading macro virus that is distributed as an e-mail attachment that, when opened, disables a number of safeguards in Word 97 or Word 2000, and, if the user has the Microsoft Outlook e-mail program, causes the virus to be resent to the first 50 people in each of the user's address books.
A Trojan horse or Trojan is a type of malware that is often disguised as legitimate software. Trojans can be employed by cyber-thieves and hackers trying to gain access to users' systems. Users are typically tricked by some form of social engineering into loading and executing Trojans on their systems.