What is the dongle that is often plugged into the back of the computer. What is it for? What is the function?

What is the dongle that is often plugged into the back of the computer. What is it for? What is the function?

 
Secret Dog is an intelligent software encryption tool for software developers. It includes a hardware installed on the parallel port or USB port of the computer, and a set of interface software and tool software suitable for various languages. The dongle is based on hardware encryption technology, and its purpose is to prevent the illegal use of intellectual property rights by encrypting software and data.
"Dog" and the dongle logo are registered trademarks of Rainbow World. Rainbow World has the largest market share in the software encryption industry, with more than 8,000 users in China. The founder of Dongle Chen Longsen, after developing the first Dongle in 1990, led his elite team to continuously improve the product and promote it vigorously. Today, "Dongle" has long been synonymous with products in the entire industry.
At present, there are already more than 10 different types of dogs on the market to protect your software to give full play to their strengths. Rainbow World has always maintained an internationally leading advantage in the promotion and application of new products and technologies. Because we believe: Bringing value to users is our value