Are registry cleaner is must for secure our PC from virus and infected files

I use CCleaner.

http://www.ccleaner.com/

The best thing to have is a automatic updating virus scan on your computer.

 Your computer will run better if you occasionally clean your  registry. In layman's terms, the Windows Registry is a hideously complex ball of string, rubber bands, duct tape and bailing wire that's supposed to keep track of Windows system settings, your hardware configuration, user preferences, file associations, system policies, and installed software. In slightly more technical terms, the registry is a database  in which Windows keeps track of relationships between hardware, software and the operating system.
 Problems with the Registry can make a Windows system slower, less reliable, unbootable, and in extreme cases can only be fixed by reinstalling the operating system.  A registry cleaner will take care of these problems.  There are free ones available on-line.  Hope this answers your question.

In my opinion, registry cleaners can mainly clean registry errors and reduce the size so as to make your computer run faster. But it can do little to get rid of viruses and infected files. You need professional anti-spyware/virus programs.

But if you need, here is free registry defrag for your reference.