The Australian Securities and Investments Commission (ASIC) has put online traders on high alert, advising them to urgently review their accounts' security, following the detection of a number of account intrusions.
ASIC issued the warning after it became aware of stockbrokers' accounts being accessed without authorisation and used to execute trades.
"A small number of accounts were impacted and in these cases the client's broker locked the accounts," ASIC said.
It did not state how it discovered the intrusions, but it is now working with online stockbroking firms to help clients who had been impacted. It is also working with authorities to identify the source of the attack.
In the meantime, ASIC is recommending users change their passwords, check their transaction history and ensure their antivirus software is up to date.
"If you become aware of any unauthorised trading on your account, you should contact your stockbroker immediately. This will help to ensure that any further unauthorised activity can be prevented."