If yes, you might be risking your computer, data, credit card information, passwords etc. to the programmers of such apps whose intentions might be to grab all that info they can for their personal benefits.
Most programmers of such apps include trojans, malware and spyware that they have written themselves and are therefore not detected by virus scanners. These trojans, malware and spyware give the crackers access to your computer and if you happen to use your computer to make payments by credit card or to do online banking, the crackers can access your credit card number, passwords and pin codes and use them to buy things.
They can even harm your computer by making them unusable. There are chances that even viruses are included!
Now one might think whats the harm in copying and pasting the serials from a website?Afterall you don't need to install anything on your computer to use them. The answer is they are no safer. The websites which host such serials are a dangerous place. Such web pages are designed to exploit security holes in the web browser, and can install trojans, malware, spyware and viruses on your computer as soon as the page is loaded in your browser.