Over 31,000 web pages carrying images of child sexual abuse have been found by a British watchdog -- but what is worse, it has also discovered that the offenders have been using bitcoins to buy the abuse images, according to media reports.
The Internet Watch Foundation (IWF) said the digital currency was accepted as a form of payment by a number of the "most prolific commercial" child abuse websites for the first time last year, Sky News reported on Tuesday.
Shockingly, the number of web pages found with images of child sexual abuse has more than doubled over the course of a year.
The number of URLs -- unique web page addresses -- hosting pictures and videos of children being sexually abused that were removed by the IWF rose from 13,182 in 2013 to 31,266 in 2014, the report said.
Between January and April last year, 37 websites selling child sex abuse images were reported as using bitcoins.
The watchdog said some of those were legitimate websites, which had been hacked.
Bitcoins are virtual currencies that enable people to pay for goods and services from their computer or mobile device independently of any bank or central authority.
Users can buy bitcoins through certain websites and create an online wallet, which can then be used for transactions.
It has its own value in hard currencies and can be bought and sold without restrictions.
However, its use has not been without controversy, and there have been numerous reports of it being used for illegal activities.
The IWF said it is working with several of the world's largest bitcoin exchanges to share intelligence and develop strategies to prevent the currency being used to distribute child sexual abuse images.
"We noticed for the first time ever last year that cryptocurrency or bitcoin was being used," said Emma Hardy, IWF's director of external relations.
"We need to ensure we engage with those who run bitcoin services, but also other ordinary payment mechanisms, financial providers, to ensure we can help prevent them being abused by criminals."
In 2013, the IWF was given new powers to seek out criminal content online in the wake of the murders of Tia Sharp and April Jones.
Both girls were murdered by men who had previously viewed child sexual abuse images on the internet.
IWF chief executive Susie Hargreaves said that while the online industry was "stepping up" efforts to tackle child sexual abuse images, many of the companies that provide services did not recognise that they had a problem, or were too slow to respond.
In its annual report for 2014, the IWF said 0.3 percent of imagery found last year was hosted in Britain, compared with 18 percent in 1996. Most of the images identified -- around 56 percent -- were hosted in North America.
Around 89 percent of the pages removed contained images of children aged 10 or under, an increase from 65 percent in 2013 and 79 percent in 2012, the watchdog added.