Most Victorians aren't sure about how to report corruption and don't believe they will be protected from any adverse consequences if they do.
While 62 per cent of 1236 people surveyed by the state's anti-corruption commission think corruption occurs, just 42 per cent think it is a problem.
Fewer than a quarter of respondents were confident about how or where to report corruption, and 80 per cent didn't believe they would be protected from any subsequent backlash.
"I'm not confident that reprisals would not occur against me or my family," one person told IBAC which released the report on Tuesday.
"Who do you report it to? And maybe that person could be corrupt too," another said.
Despite these fears, three-out-of-four people said they would report corruption - such as bribery, kickbacks and the misuse of confidential information - if they witnessed it.
But fewer than half of respondents thought a public servant using a work credit card to pay a personal taxi fare was corrupt conduct.
IBAC chief executive Alistair Maclean said the report showed more work was needed to explain how to report public sector corruption and what protections were available.
"It's concerning that there are low levels of confidence in the protections provided to those reporting corruption," he said.
WHAT VICTORIANS THINK OF CORRUPTION
* 62 per cent agree corruption occurs in Victoria
* 42 per cent think it's a problem
* Fewer than 25 per cent know how and where to report it
* 39 per cent feel they will face personal costs if they speak up
* 56 per cent agree they have a responsibility to prevent corruption
* 25 per cent think meaningful action will be taken
Source: Independent Broad-based Anti-corruption Commission