The corporate regulator has revealed a second instance of inadvertently blocking large numbers of websites while trying to shut down access to investment scams.

The Australian Securities and Investments Commission (ASIC) has the power to block access to internet sites being run by investment fraudsters.

ASIC deputy chairman Peter Kell has told a Senate hearing such powers have been used 10 times over the past 12 months.

But ASIC's actions have come under public scrutiny recently, after it admitted to inadvertently blocking access to more than 1,000 legitimate sites.

Mr Kell last night revealed separate action taken in March also had unintended consequences.

"A very small number of active sites - around 1,000 - were temporarily affected," he said.

Mr Kell said ASIC was talking with law enforcement agencies and major internet providers about how to better target its actions "so that we can best determine how we can continue to disrupt these criminal websites without impacting on legitimate sites."

He also said the regulator would be more transparent about its use of powers to block access to scam websites.