• His parliamentary office in Wellington was broken into on September 16 last year. Police investigated and swept the office for bugs but none was found.
• His Rodney constituency office in Orewa was broken into in early October and a laptop and two phones were taken. Police investigated but no arrests have been made.
• His personal email was hacked.
The revelations come after the release of Nicky Hager's book Dirty Politics, which claims that National colluded in smear campaigns by right-wing blogger Cameron Slater.
Political commentator Chris Trotter said MPs having their property stolen was "not something that we're used to in New Zealand politics".
"It's something we tend to associate with incidents like the Watergate break-in and that scandal.
"No one would condone the organised theft of political information, it puts the whole system at risk."
Hager's book is based on six years of emails apparently taken from Slater's Gmail and Facebook accounts.
Watch: Key responds to Hager book 'Dirty Politics'
Slater says he will complain to police about his Whaleoil website being hacked and will name Kim Dotcom as someone police should speak to.
Mitchell has had his own run-in with Dotcom. They had a confrontation at a barbecue last August.
Mitchell also confirmed he was helping some constituents who had issues with Dotcom but for privacy reasons, could not give details.
Hager told the Herald on Sunday that he did not know about the break-ins.
"Every leak in history in every country has come from an authorised source ... they're from a place where they were not authorised and the people who are leaked about, who are embarrassed, always go on about the fact they were illegitimately gathered, but that's what a leak is," he said.
Hager added he wanted to make his source material public, but it was "tricky".
Dotcom told the Herald on Sunday last night that he had been meeting lawyers to seek the source material from Hager's book.
He claimed the book amounted to collusion in a smear campaign against him and the Internet Party.
"There has been many suggestions made to me that National is behind it and now with Hager's book there is enough information out there to take it to the courts and get discovery from the National side and see how deeply they were involved and what their role is in that smear campaign," he said.
Meanwhile, Labour leader David Cunliffe demanded an apology from Prime Minister John Key yesterday, after releasing an email he said confirmed National was involved in breaching Labour's website server.
National dismissed the allegations, saying it was "old news" and accused Cunliffe of helping Hager conduct a smear campaign.
