Worms are programs that send copies of themselves from one device to another over a network. Some worms also perform harmful actions on an affected device.
Many worms are designed to appear attractive to a user. They may look like images, videos, applications or any other kind of useful program or file. The aim of the deception is to lure the user into installing the worm. Other worms are designed to be completely stealthy, as they exploit flaws in the device (or in programs installed on it) to install themselves without ever being noticed by the user.
Once installed, the worm uses the device’s physical resources to create copies of itself, and then send those copies to any other devices it can reach over a network. If a large quantity of worm copies is being sent out, the device’s performance may suffer. If many devices on a network are affected and sending out worm copies, the network itself may be disrupted. Some worms can also do more direct damage to an affected device, such as modifying files stored on it, installing other harmful applications or stealing data.
Most worms only spread over one particular type of network. Some worms can spread over two or more types, though they are relatively rare. Usually, worms will try and spread over one of the following networks (though there are those that target less popular channels):
- Local networks
- Email networks
- Social media sites
- Peer-to-peer (P2P) connections
- SMS or MMS messages