Viruses and Worms (Propagation)

• Virus: attaches to a host file or program; spreads when the host is executed. Requires user or host action.
• Example: classic PE file infectors that prepend/append code to executables.
• Worm: self-propagating; spreads across networks without a host program.
• Example: WannaCry (2017) used the EternalBlue SMB exploit to spread worldwide in hours.
• Key distinction: a worm does not need you to run anything — it finds and infects the next host itself.