Microsoft search engine Bing has introduced a "pop-up" warning to tell UK users they are searching for illegal child abuse images.
Searches for the inappropriate material will trigger the Bing Notification Platform message warning.
The pop-up tells browsers the content they are looking for is against the law and provides a link to a counselling service.
It is triggered by search terms on a list provided by the The Child Exploitation and Online Protection Centre (CEOP).
Prime Minister David Cameron this week threatened to impose tough new laws on internet giants if they fail to blacklist key search terms for horrific images by October as part a crackdown on online porn .
A Microsoft spokesman said: "If someone in the UK tries to use search terms on Bing which can only indicate they are looking for illegal child abuse content, they will activate the Bing Notification Platform which will produce an on-screen notification telling them that child abuse content is illegal.
"The notification will also contain a link to Stopitnow.org who will be able to provide them with counselling.
"Due to the unique and sensitive nature of child abuse and child exploitation, Microsoft has been, and remains, a strong proponent of proactive action in reasonable and scalable ways by the technology industry in the fight against technology-facilitated child exploitation.
"The Bing Notification Platform is just one way in which Microsoft is working to tackle the scourge of online child abuse content.
"In addition, we have teams dedicated globally to abuse reporting on our services and the development of new innovations to combat child exploitation more broadly."
Microsoft said it already has a policy of removing links to illegal content as soon as possible.
Andy Baker, CEOP's deputy chief executive, welcomed the creation of the device but said it was the first step towards blocking access to the illegal images and videos, and protect children.
He called on the industry to "take ownership" of the problem.
"While the Bing project isn't the whole solution, I hope it goes some way to making those who are curious about searching for indecent images think again," he said.
"As part of our day-to-day work at CEOP we monitor the behaviour of offenders, including how they search for indecent images and the kind of language they use, which puts us in a good position to provide industry with a list of search terms as also outlined by the Prime Minister in his speech on Tuesday.
"Anything which prevents people accessing indecent images of children and stops more children from being harmed, can only be a good thing but much more is needed and the industry must play their part and take ownership of this problem."
Research by Experian last December showed that Bing had a 4.99% share of the UK search engine market, which is dominated by Google and its 88.3% market share.
A Google spokesman said: "Child abuse imagery is illegal and we have a zero tolerance policy to it.
"We use purpose built technology and work with child safety organisations like the Internet Watch Foundation to find, remove and report it, because we never want this material to appear in our search results.
"We are working with experts on effective ways to deter anyone tempted to look for this sickening material."