Banksy's festive artwork highlighting homelessness has been preserved in Birmingham.
Plastic covering the reindeer painted in the city's Jewellery Quarter was attached by wall owners Network Rail.
Within hours of its Instagram unveiling, featuring a man named Ryan, someone leapt over barriers and sprayed red noses on the two reindeer.
The Jewellery Quarter Development Trust (JQDT) said the work was "important to protect."
A film on the artist's social media, showing a man on a bench being "pulled" by the reindeer, has been viewed almost 3m times.
Barriers were later installed around the piece in Vyse Street, but a person managed to jump them and deface it on Monday.
David Golding, of Network Rail, said: "As a railway family our hearts go out to the homeless, especially at this time of year.
"Banksy's wall art has captured their plight so well. It's right we protect it so everyone can see it.
"We discourage any graffiti and we spend a lot of time removing it from around the network… but it's not every day we get a bona fide Banksy."
Luke Crane, the executive director of the JQDT, said it wanted the artwork to remain and was "keen to protect and preserve the piece".
"It can have a real impact on the community by keeping Banksy's message of homelessness," he said.
Mr Crane said a man aged 25 to 30 wearing a grey hoodie, jeans and trainers "casually walked off" after he sprayed the noses red.
However, Banksy art collector John Brandler said he did not feel the work's integrity had been compromised by the intruder.
"Shouldn't Rudolph have a red nose? Maybe Banksy forgot it," he said.
"It's not as if it's been tagged. It's an amazing piece, although I do think it needs to be removed to protect it otherwise there's a good chance it will be vandalised and lost."
Unveiling the work, Banksy had praised the generosity of people who gave Ryan food and drink while they filmed.
The post said: "God bless Birmingham. In the 20 minutes we filmed Ryan on this bench passers-by gave him a hot drink, two chocolate bars and a lighter - without him ever asking for anything."
Youth charity Centrepoint said "art is a great way to highlight the issue" of homelessness.
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