Viruses - require some sort of human interaction and are often transmitted by USB sticks or other
portable devices. When the program is executed, they replicate themselves by inserting their own
code into other programs. Macro (document) viruses: Written in Macro Languages; embedded in other
documents (Word, Outlook). Boot Sector viruses: infects the PC's boot sector or the Master Boot
Record, ensuring it runs every time the PC boots. Stealth Viruses: try to hide themselves from the
OS and antivirus software. Polymorphic Viruses: change their signature to avoid the antivirus
signature definitions. Well-written polymorphic viruses have no parts that remain identical between
infections, making it very difficult to detect directly using antivirus signatures. Multipart
(Multipartite) Viruses: spread across multiple vectors. They are often hard to get rid of because
even if you clean the file infections, the virus may still be in the boot sector and vice-versa.