Win HDD is malicious software that pretends to be a system optimization tool but actually is one more fake program. The main purpose of it is selling a fake license of Win HDD and of course gaining money for it.
Once inside the system, the program uses very well-considered tactics. First, I should mention that Win HDD is installed with a help of Trojan viruses. Then the program attempts to imitate functions of system optimization tool. It simulates system scan and reports about tons of critical errors detected on your machine. for fixing that you will be offered purchasing Win HDD.
Besides the scan that you didn't even ask for, Win HDD will annoy you with plenty of pop up ads and security notifications that will be stating one and the same - your system is infected with spyware and you need to register your copy of Win HDD in order to fix the infections. Ignore them no matter how convincing they would look like. Your system probably is completely clean. Win HDD is definitely not a reliable application.
As you probably understood, Win HDD is not a program to keep in your system. It only slows your computer down and makes it easier for spyware to enter your system. The best solution for the victims of Win HDD is getting a reliable anti-spyware program and removing it together with other spyware that could infect while Win HDD was running. You can also use removal instructions of Win HDD and get rid of it manually.