The Austrian minor is accused of attacking three websites per day on average. He has confessed to the crime, according to the Austrian federal criminal police office.
The federal criminal police office statement says (translated from Austrian-German via Google translate) the 15-year-old is the youngest hacker to be arrested in that country.
Interior Minister Johanna Mikl-Leitner said: "This case shows both how vulnerable our computer systems are, and on the other hand, it also shows how computer and technologically adept the youth of today are."
The Austrian police allege that he scanned websites to capture user data and login credentials. Police allege that he then published the sites' weaknesses online and via Twitter.
He is also suspected of accessing some sites and making alterations to the appearance of some web pages.
"While it may seem obviously to be a prank, it is not a petty offense," said Mikl-Leitner.
The Austrian police statement says that while most web crime is committed by people over the age of 25 (46%), 11% of these crimes are committed by 10 to 21-year-olds, 17 percent by 21 to 25-year-olds.
The police say they will focus on prevention workshops in schools to educate Austrian children about the flaws and benefits of the web.