A site purporting to speak for the group said newly enacted laws that could mean jail for anyone downloading copyrighted music and movies "will result in scores of unnecessary prison sentences to numerous innocent citizens".

The finance ministry's website came under attack on Tuesday, with a number of webpages defaced, ministry official Takanari Horino told AFP, and websites of the supreme court and intellectual property high court were also down for a short time overnight, he said.

"We are investigating where the illegal item came from," the official said, referring to an unauthorised link posted to the ministry site.

"We are aware of the Anonymous statement referring to the new copyright law, but we don't know at this point if the cyberattacks are linked to the group," he said.

The anonpr.net website said laws passed by both houses of Japan's parliament last week would do "little to solve the underlying problem of legitimate copyright infringement.

"The content industry is now pushing ISPs in Japan to implement surveillance technology that will spy on... every single Internet user in Japan," it said.

"This would be an unprecedented approach and severely reduce the amount of privacy law abiding citizens should have in a free society."

The statement also warned the government and country's Recording Industry Association to "expect us the same way we have come to expect you in violating our basic rights to privacy and to an open Internet".

A Wednesday morning post on Twitter by user @op_japan claiming to speak for Anonymous said: "Good morning #japan. Expect more from us today! #anonymous #opjapan #anonfamily #freeanons."

It gave no further details.

A spokeswoman for the Recording Industry Association said on Wednesday no attacks on its website had been recorded, but that it was investigating the issue.

The new copyright law stipulates that "downloading of copyrighted works knowing that they are not free and that it is illegal" will lead to a prison sentence of up to two years, or a fine of up to two million yen (25,300 dollars), or both.

Some 4.36 billion files, including music and movies, were illegally downloaded in 2010, 10 times the number of legally downloaded music files, the association said.

Anonymous is a "hacker-activist" network that has claimed online attacks on sites ranging from the Vatican to Los Angeles Police Canine Association, but is increasingly the target of police who have arrested dozens of members.

The joint report by Guardian Analytics and McAfee said "Operation High Roller" was led by criminals attacking cloud-based servers in a global fraud campaign.

The report from the two US firms said the attacks tried to steal between $75 million and $2.5 billion (60 million to two billion euros) from at least 60 banks worldwide.

The ring used "sophisticated" techniques including automation and targeted high-value accounts in Europe before moving to Latin America and the United States, it said.

"This is a serious new threat that is actively targeting American financial institutions," a statement from Guardian Analytics said.

"To the best of our knowledge the scheme has already netted nearly $80 million worldwide, and it could be much higher."

The report offers insight into hacking into banks, which is often not disclosed by financial institutions.

"As this research study goes to press, we are working actively with international law enforcement organizations to shut down these attacks," the report said.

In the attacks uncovered earlier this year, the criminals "attempted transfers to mule business accounts as high as 100,000 euros," the report said.

"Where Europe has been the primary target for this and other financial fraud rings in the past, our research found the thefts spreading outside Europe, including the United States and Colombia."

In the United States, "victims were all companies with commercial accounts with a minimum balance of several million dollars."

In most cases, the victims were found through online reconnaissance and "spear phishing," which uses a fake email to get an account holder's login details and password.

The first attacks affected "a popular bank in Italy and its consumer and business accounts" and used SpyEye and Zeus malware to transfer funds to a "mule account" or pre-paid debit card where the thief could retrieve the funds quickly and anonymously.

But later attacks showed increased automation and sophistication, in some cases taking over the victim's account without an attacker's active participation. In some cases, the criminals were able to bypass smartcard readers which offer extra authentication used in many European banks.

"This ring adds many breakthroughs: bypasses for physical 'chip and pin' authentication, automated mule account databases, server-based fraudulent transactions," the report said.

It said the attacks hit "every class of financial institution: credit union, large global bank, and regional bank."

In some attacks, transactions were routed through a server in California, but the researchers said they "found evidence of the fraudster logging in from Moscow, Russia, to manipulate some of the transactions."