WELLINGTON, New Zealand (AP) -- Foreign spies have hacked into New Zealand government computers in recent months but no classified information was stolen, Prime Minister Helen Clark said Tuesday.

Clark's attempt to reassure followed revelations by the country's top spy, Security Intelligence Service head Warren Tucker, that foreign sources had hacked into government computer systems and stolen information.

Later checks found hard-to-detect software had been installed that could be used to seize control of computer systems.

He said there was "strong evidence" that foreign governments were responsible for the attacks and while he did not name countries, Tucker referred to comments by Canada's security service about Chinese spying activities, The Dominion Post newspaper reported Tuesday.

Clark said she knew which governments were involved, but declined to name them. The issue has not been taken up with the countries in question.

"That's not the way intelligence matters are handled," she said. "It's not something unique to us, it's something that every country is experiencing."

Last week China was accused of hacking into German and U.S. government computer systems.

Russia and China also have been implicated in attacks on the British government's computer system.

Some departments didn't even realize their systems had been breached, Tucker said, adding that sensitive information was stolen and attempts had been made to access classified data.

He said that in one attack, a program was installed to generate bogus but genuine looking e-mails.

But Clark moved to quell concerns that foreign spies had made off with sensitive data.

"The assurance I've been given by intelligence agencies is that no classified information has been at risk at all," she told reporters.

"Now we have very smart people to provide protection every time an attack is tried," she said. "What I can stress is that absolutely no classified information has ever been penetrated by these attacks."