No, the software doesn't harm your system since it only copies its own players and codecs. However, special situations might appear when compatibility with the other installed apps and operating system is not known. Practically, this can't be checked since every computer is different due to the installed apps, OS version, antivirus protection, hardware components etc. In case something bad happens after you install K-Lite Codec Pack, restart the computer and press F8. Go to Safe Mode and then remove K-Lite and use something else instead.