Can someone explain the meaning of "whisper blowing" in an anti corruption material? Thanks a lot?

The term is Whistle Blowing.

It means to notify the police, or otherwise expose an illegal activity which you are aware of.

This frequently puts the career (and health) of the person who is blowing the whistle at risk because they are usually employed by, or work with the people committing the crime. Whistle blowing laws exist to protect these people from the repercussions of tipping off the police.

or do you mean whistle blowing?

http://en.wikipedia.org/wiki/Whistleblower