I've seen a few posts on here where people have had amounts appear in their bank accounts and have wondered whether they should keep it or give it back. Looks like it's definitely looked upon as fraud…
http://www.abc.net.au/news/2016-05-05/woman-arrested-at-sydn…
Apparently a Sydney woman either found 4.6 million in her bank account, or was able to overdraw her account by 4.6 million back in 2012 and has been arrested for fraud after trying to leave the country.
According to the police prosecutor, the money was accessed through an overdraft facility, mistakenly attached to a Westpac savings account.
In addition to a charge of obtaining financial advantage by deception, she was also charged with knowingly dealing with proceeds of crime.
Bottom line, from the article:
Sydney City Police Detective Inspector Sean Heaney said if members of the public find money in their accounts that should not be there, or they have an ability to overdraw on an account that they should not have, they should not spend the money.
He said exploiting an error made by the bank amounted to stealing.
"The money doesn't belong to you, you know that, don't go spending it, it's going to cause you some trouble with the police.
How is my comment a personal attack? I was saying the same thing as you about Westpac, but giving a live example of the incompetency of the staff!