Computers are devices that people use to create and manipulate local files and interface with other people via the internet. Computers are capable of doing all sorts of things, depending on the capabilities of the specific computer and the savviness of its user. One of the main things people do with computers is make websites.
The vast majority of computers are not directly used by people at all. Most are servers, i.e. the computers that send files to people and other computers that are using the internet. Because of their crucial role in making the internet happen, computers are complicit in everything the internet does—from commercial, nominally acceptable functionalities like search via Google and access to propaganda and misinformation via Facebook to illicit applications like hiring hitmen and the distribution of child pornography.
Even the most mundane interaction between computers and the internet results in websites. These beget all manner of ills, like Javascript, popup ads, ecommerce, and startup companies. Inexperienced operators of computers can easily find themselves vulnerable to scams and "viruses," which are softwares with predatory purposes.
As long as computers stay clear of the internet, they can mostly only produce spreadsheets and slideshows. These are essentially benign.
In governmental and industrial applications, computers are even more dangerous—they might be used to pilot murderous drones in foreign countries or even produce video games.
Because of their wide range of applications, we consider computers to be fairly dangerous.
