Anonymous hackers have posted data taken during its January cyber raid on KPN, allegedly proving it had access to the Dutch internet service provider's (ISP) networks.

News of the attack on KPN first arose in January after the details of 500 customer accounts were posted online.

Following the post, on 10 February KPN issued its own statement confirming it had disabled all two million of its clients email addresses as a response to the security breach. "KPN email has been disabled as a precaution due to a digital break-in," read KPN's statement.

The attack has since been credited to Anonymous, after several Twitter accounts associated with the collective tweeted statements claiming responsibility for the attack.

Following on from this after KPN blocked the accounts, the collective re-posted data allegedly taken from KPN to prove it still had access to the company's network.

"Dutch TELECOM+INTERNET infrastructure hacked by anonymous TELECOM GIANT'S #KPN 2-mil email BLOCKED" read one tweet by Anonymous Press.

Analysts examining the data have since suggested Anonymous's claim may be authentic, recommending KPN clients should change their passwords.

"On January 20 it was discovered that there had been a breach and they worked hard to fix the problem. A week later it turns out that their efforts were unsuccessful and the attackers still had access to the environment," read a post by the Internet Storm Centre's Mark Hoffman.

"If you are a KPN client you'll want to change your passwords and if your password is used anywhere else you'll want to change those as well."

The attack is one of many mounted by Anonymous in the Netherlands. Prior to its KPN raid the collective had enacted a coordinated spamming campaign against pro-censorship, artists rights group Brein.

The attack followed Brein's court room victory to have access to The Pirate Bay blocked by several ISPs. As well as the spamming campaign Anonymous also posted another statement on Pastebin listing the contact details of several high-up employees within the entertainment industry.

The statement came with a request for all anti-censorship protesters to contact the Brein employees and supporters and voice their discontent.