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The government also is investigating who was behind the hack, though that may be difficult to verify without help from Tehran.

An unknown hacker who claimed responsibility for a similar breach of U.S.-based certificate issuer Comodo Inc. in March, has also claimed responsibility for the DigiNotar hack.

In a posting on Pastebin.com under the handle “ComodoHacker” on Monday, he or she offered a user name and password for an administrator’s account at DigiNotar as evidence.

The post also boasted of having hacked four other “high profile” certificate providers, including GlobalSign.

GlobalSign takes this claim very seriously and is currently investigating,” the company said in a statement.

“ComodoHacker” has used phrases in the Farsi language spoken in Iran in previous posts to Pastebin _ including a phrase that also was found by Fox-IT in a message left on DigiNotar’s servers. Monday’s post cited anti-Dutch political motivations for the attacks.

Donner said that in the wake of the incident the Dutch government is considering legislation that would make it mandatory for companies to disclose computer hacks and data leaks.