A guide to "secret sexting codes" has gone viral on Facebook after police in Ireland shared it to help parents spot signs of child sexual exploitation, according to reports.

The guide - showing an array of acronyms and abbreviations used by teenagers in sexual text - or sext - messages originated in the United States and was shared on the social network by Northern Irish police team PSNI Newry and Mourne.

It has been shared nearly 4,000 times.

The guide reveals that LH6 stands for "let's have sex" while the number 8 apparently represents oral sex, said Britain's Independent.

There are various terms to alert the other person in a conversation that a parent is around, including MOS (mum over shoulder), P999 (parent alert) or PAL (parents are listening), and even KPC for "keeping parents clueless".

Parents should be horrified if they find the abbreviation NIFOC on their child's feed, as it apparently stands for "naked in front of computer", while IWSN means "I want sex now" and "GYPO" is short for "get your pants off".

In addition to sexting terms, the guide also reveals references to drugs such as "420" for marijuana, said the Independent.

Some teens claimed not to know the codes, while adults commenting on Facebook were horrified.

The police force said in another Facebook post: "Some of the codes may not be being used here but it is something to be aware off if you see cryptic messages on your kid's devices.

"Also, prevention is better than cure, so speak to your kids about their online activity, what they are using and respect the age limits of social media platforms."

While snooping on teenager's conversations may be considered a violation of their privacy by some, police have stressed the need for vigilance to protect children from online grooming, the Independent said.

Britain's National Society for the Prevention of Cruelty to Children has found that one in seven youngsters have taken a naked or semi-naked picture of themselves - with more than half going on to share this image with another person, the Independent reported.

The NSPCC claims one in five indecent images shared of children online are taken by the child themselves, and then shared without their consent.