A 41-year-old Houston man was arrested on suspicion of child pornography charges in an investigation founded on a tip that Google sent to the National Center for Missing and Exploited Children.

"They got a tip, basically Gmail," detective David Nettles of the Houston Metro Internet Crimes Against Children Task Force told a local news broadcast last week.

The defendant, John Skillern, was being held on $200,000 bond and is a registered sex offender connected to a 20-year-old sexual assault on a young boy.

Google publicly promised last year to help crack down on online child pornography. Eric Schmidt, Google's executive chairman, said in November 2013 that Google "put more than 200 people to work developing new, state-of-the-art technology to tackle the problem."

Schmidt said that while Google algorithms are not "perfect," they had removed child porn results from more than 100,000 search queries. When objectionable material is found, engineers assign the image or video a digital fingerprint that can prevent it from re-appearing in results and can make it simple for automated systems to spot.

In an editorial in the Daily Mail last year, Schmidt said that this work went further than search.

"That's why internet companies like Google and Microsoft have been working with law enforcement for years to stop paedophiles sharing illegal pictures on the Web," he wrote. "We actively remove child sexual abuse imagery from our services and immediately report abuse to the authorities. This evidence is regularly used to prosecute and convict criminals."

Gmail is the world's biggest e-mail service with more than 450 million global users. It is in the midst of a privacy flap over the search engine automatically scanning Gmail messages for a variety of reasons, including the delivery of ads. In an ongoing US federal lawsuit, Google is accused of breaching federal and state privacy laws, including wiretapping statutes, through this monitoring.

Child pornography enjoys no First Amendment protections.

Google, in a statement, said it was following the law, which requires ISPs to out those moving child porn to the National Center for Exploited Children:

Sadly all Internet companies have to deal with child sexual abuse. It’s why Google actively removes illegal imagery from our services—including search and Gmail— and immediately reports abuse to NCMEC. This evidence is regularly used to convict criminals. Each child sexual abuse image is given a unique digital fingerprint which enables our systems to identify those pictures, including in Gmail. It is important to remember that we only use this technology to identify child sexual abuse imagery, not other email content that could be associated with criminal activity (for example using email to plot a burglary).

However, the law does not require ISPs to scrape electronic messages for images of child porn, as Google does.

The National Center for Missing and Exploited Children declined to immediately say how may tips it has gotten from ISPs regarding smut found in e-mail: