LONDON — Police in the capital are investigating a case of cyber flashing after a woman received images of a man's penis via the Airdrop function of her iPhone.

Lorraine Crighton-Smith, 34, was travelling to work in south London when the indecent images popped up on her phone. She had set the device to be visible to anyone, not just contacts, which allowed the stranger to send the unwanted pictures.

Although she was forced to see the images, she didn't accept them, which meant British Transport Police couldn't investigate the issue further.

See also: A British rail worker just answered all your burning questions about train travel

Crighton-Smith explained how she received the images. "I had Airdrop switched on because I had been using it previously to send photos to another iPhone user - and a picture appeared on the screen of a man's penis, which I was quite shocked by," she told the BBC's Victoria Derbyshire programme.

"So, I declined the image, instinctively, and another image appeared, at which [point] I realised someone nearby must be sending them, and that concerned me. I felt violated, it was a very unpleasant thing to have forced upon my screen."

"I was worried then about who else might have been a recipient, it might have been a child, somebody more vulnerable than me. My name on Airdrop just says Lorraine's iPhone so they knew they were sending it to a woman. The images were of a sexual nature and it was quite distressing."

British Transport Police say they haven't encountered this problem before, but have been aware of a similar thing happening via Bluetooth. Superintendent Gill Murray insisted they have a dedicated team to deal with such issues and will arrest any offenders.

"We have a dedicated Cyber Crime Unit who can analyse mobile phones and track data transfers back to suspects' devices," she said in a statement provided to Mashable. "By linking this to physical evidence, such as CCTV footage or witness statements, we can catch offenders and bring them to justice through the courts." "My message to offenders is clear, while you might think you can hide behind modern technology in order to carry out abuse, you leave a digital footprint and stand a very good chance of being caught, arrested and ending up on the sex offenders register."

"Cyber flashing is new but if you do it, you will be arrested " says Superintendent Gill Murray from @BTP http://t.co/W9BbSAPxL3 — Victoria Derbyshire (@VictoriaLIVE) August 13, 2015

Murray advised anyone who's experienced sexual harassment of any kind on their travels to report it by texting 61016, which will alert transport police.

The British Transport Police told Mashable that crimes of this nature fall under the Malicious Communications Act of 1988, which covers all types of communication from phone messaging to physical letters, and so they can't say exactly how many offences have occurred. They're investigating whether anyone has been successfully prosecuted for sending explicit photos via Bluetooth or Airdrop.