Actress Sienna Miller appears to have become the latest celebrity to have fallen victim to hackers who claim to have shared X-rated photos of her online.

The images are alleged to be of the 35-year-old British star topless while wearing a mask over her face.

It is understood they have been released by cyber-hackers who access cloud storage accounts and social media sites belonging to celebrities and their friends.

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Leaked: Actress Sienna Miller appears to have become the latest celebrity to have intimate pictures stolen by hackers and posted online

A source told The Sun: 'Sienna will be devastated these pictures said to be of her fooling around have been put online by some weirdo.'

In previous incidents involving A-list celebrities, the hackers traded the pictures with each other online to for website hits and notoriety.

Harry Potter star Emma Watson, 26, also faced reports of leaks of private pictures.

While Holly Willoughby has also reportedly been threatened by hackers who claim to have obtained 'X-rated photos' of the This Morning host for 'humiliation' online.

New reports claim that 36-year-old Holly has had online content 'stolen' and threatened for reuse.

Caught up: Emma Watson was forced to issue a statement last week, to deny claims that nude pictures of her were circulating online

Targeted? Holly Willoughby has been named as the latest star in a list of 'dozens' reportedly hacked by online trolls who are threatening to publish 'X-rated' pictures of the star

The Sun recently published claims that Holly and Millie are just two of 'dozens' more celebrities - including Keeping Up With The Kardashians star Kylie Jenner - to be targeted by trolls.

Hackers are said to have 'guessed passwords of stars' social media accounts,' thus intercepting their private messaging services to torment them about the existence of bait they could use for online forums.

MailOnline has contacted representatives for Holly Willoughby, Kylie Jenner and Millie Mackintosh, following the claims.

Personal images: Millie Mackintosh is also reportedly being targeted with the threat of pictures trolls want to use for 'humiliation', a new reports suggests

Intercepted? According to the new reports, social media profiles of those including Kylie Jenner have been tapped into after guessing passwords

Despite the reports, a source close to Holly went on to deny the existence of the pictures, telling the newspaper: 'Holly is unconcerned as these are baseless accusations as far as she is concerned.'

One of the British stars targeted in a leak earlier this month, included former child star and Harry Potter actress Emma.

Personal pictures of the Beauty And The Beast leading lady taken during a swimsuit fitting were said to have been leaked onto the 'dark web' last Tuesday after her computer was reportedly hacked.

Not threatened: Sources close to Holly claim there are 'no such nude pictures'

Fruitless: While it's not clear where the pictures of Holly (here in her younger, presenting days in 2004) are alleged to have come from, she is not said to be worried about the leak

Empty threats: Holly is one of Britain's best known presenting talents - with over two decades in the industry (here in 2004)

Directly addressing the issue, Emma denied that pictures in the same post - featuring an unknown woman in the bath with her face cropped out - were her.

In a statement released in response, Emma's team said: 'Photos from a clothes fitting Emma had with a stylist a couple of years ago have been stolen.

'They are not nude photographs. Lawyers have been instructed and we are not commenting further.'

Private: Millie is still best known for her role in E4 reality show Made In Chelsea

Cheeky: On Instagram, the brunette chooses what she puts into the public eye with consideration but also a cheeky sense of humour (pictured)

Violation: Stars already targeted with the action have sought legal advice over similar alleged hacks

Meanwhile, Hollywood actress Amanda - who is pregnant with her first child - has also threatened a website with legal action if they don't take the images down.

A letter from her legal team, seen by website TMZ, states: 'Several very private photographs of Ms. Seyfried either in various states of nudity or in intimate moments with her former boyfriend (the 'Seyfried Photographs') have been reproduced and posted.'

The batch of images of Amanda are also believed to have been posted on 'the dark web', a matrix of encrypted websites that allow users to surf with anonymity.

Taking action: Amanda Seyfried - who's pregnant with her first child by Thomas Sadoski (pictured) - faces resurfaced intimate images from her relationship with Justin Long

The intimate photos that were stolen are from her time with actor Justin Long, whom she dated from 2013 to 2015.

It is unclear if the photos were stolen from Long or Seyfried's device.

Last month, a 29-year-old Chicago man was jailed for nine months for hacking into the electronic accounts of celebrities - including Jennifer Lawrence - on Apple's iCloud service, and stealing private information including nude videos and photos.

Dozens of stars' photos were posted online as part of the 2014 phishing exercise, including shots of Rihanna, Kate Upton and Kirsten Dunst. Apple admitted a 'targeted attack,' but denied its cloud storage system had been breached.