In Poland there was a case few years back of a company (I have no idea if that means a one person company or a bigger one) owner finding out by putting a name of his client into google that it indexed documents containing private information of over a 1000 of companies that are clients of PKO BP and reported it to the bank.

At first the bank security department said no one will find it so it's safe and later when he pressed the issue as a dangerous leak they reported him to the police for "hacking and extortion". All the computers from his company got confiscated for investigation so he had to buy new computers and software to continue running his company. In the end he was found not guilty by the police investigation of his computers so the prosecution dropped the case (it didn't even go to court) and all his stuff returned after 6 months.

Source in Polish (sorry, there is no English source): https://niebezpiecznik.pl/post/glebokie-ukrycie-danych-w-pko... http://www.tvn24.pl/wiadomosci-z-kraju,3/haker-mimo-woli,132...

Bank spokesperson later explained that the files were "deeply hidden" ("głębokie ukrycie", he said it's an IT term, it's not) and only one person found them in 4 years of their existence there so it's not a big deal.

And in general misusing, testing, etc. a website is illegal without owners permission, there is now a small exception for acting in good faith but it's narrow, a bit strangely worded and it doesn't prevent stuff like above.