Worms are in the same family as Trojans but have significant functions that separate them from normal viruses. Trojans are the way they are because they usually need some sort of social engineering to get victims to run them. Worms are similar because they usually rely on social engineering to strike systems.
Worms are so dangerous because of their ability to multiply and spread. Worms can be spread in many forms which makes them a deadly weapon when wanting to create a Botnet. Networks, security holes, file sharing, social networks, and external devices are all things worms can infect and use to spread. They are usually first initiated through phishing attempts but once one system is under effect, many more will fall.
Not only can worms multiply and spread quickly but they can perform many malicious actions. Most commonly they will drop malware like spyware or ransomware. Worms can also delete files, steal data, deplete hard drive space, and overload networks.
Don’t mistake a virus for a worm. While the two share many similarities they are completely different because of one thing. Viruses rely on human actions to execute commands while worms can simultaneously act without needing someone to activate it.
Hackers can “manipulate” the worm’s ability to act simultaneously. Letting the worm spread through many computers connecting them all in a web-like form. This is known as a botnet. All the infected computers in this web-like structure can be controlled by a hacker (assuming the worm drops a malware on each computer) This allows hackers to have the ability to crash networks or websites with network traffic. For example, an entire hospital’s network can be shut down if hackers focus their botnet on it.
Like most forms of malware, worms can be stopped if security measures are taken. Anti virus or anti malware along with safe computer practices like caution with suspicious emails or text can almost guarantee safety from things such as worms.
Source:
https://www.malwarebytes.com/computer-worm