Business Technology

Sunday 21 September 2014

Why Google scans your emails for child porn

Google trawls both the public internet and your private data

Matthew Sparkes

Published 04/08/2014 | 13:48

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Tuesday 14 May 2013. Google HQ, Dublin 2.
Google’s current headquarters in Dublin

A convicted sex offender has been arrested after Google flagged images of child abuse found in his Gmail account to authorities, according to reports, revealing that the search giant is quietly but methodically watching our email activity for illegal images.

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Google spotted that the man had illegal images of a young girl stored in his Gmail account during an automated search and reported it to the US non-profit National Center for Missing and Exploited Children. A subsequent police investigation lead to his arrest.

Detective David Nettles of the Houston Metro Internet Crimes Against Children Taskforce told Channel 11: "He was keeping it inside of his email. I can't see that information, I can't see that photo, but Google can. He was trying to get around getting caught, he was trying to keep it inside his email.

"I really don't know how they do their job. But I'm just glad they do it," he said.

Google told The Telegraph that it would not reveal technical information on any individual case or give exact details of the nature of the searches that it carries out.

But we know from previous reports that Google’s automatic image search works by comparing “hashes” of images, rather than the files themselves. A hash is a unique code created by running an image through a simple algorithm. The hash of each file is then compared to a database of hashes produced by known images of child abuse – any match is an almost certain indication that the account being searched contains an illegal image. Working in this way negates the need for Google to maintain a large database of illegal images themselves, which would be legally problematic to share with third parties.

To this end, Google co-funds the Cambridge-based charity the Internet Watch Foundation, whose mission is "to minimise the availability of 'potentially criminal' internet content, specifically images of child sexual abuse (including child pornography) hosted anywhere, and criminally obscene adult content in the UK".

The IWF can supply a list of hashes of known or suspected illegal content online to third parties so that it can be blacklisted from other search engines or services, and runs a reporting hotline to allow people to report links or files. Google also runs its own searches and contributes to this list.

Google has hinted in the past that it performs searches on content, although did not elaborate on whether this was public or private data. An article in The Telegraph last year by the company’s chief legal officer David Drummond said: “since much of this illegal material is circulated repeatedly - making the crime infinitely worse for the victims - we have built technology that trawls other platforms for known images of child sex abuse.”

Until now it has never been confirmed that Google trawls information that is not on the public internet, but is contained within our private accounts such as Gmail email messages.

Although few would argue that tracking down those who collect, store or transmit images of child abuse is important work, it will also raise privacy concerns for those who feel uneasy about Google searching through every image they send via GMail.

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