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Size doesn’t matter: Just a small number of malicious files can corrupt LLMs of any size

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Size doesn’t matter: Just a small number of malicious files can corrupt LLMs of any size


Overview of our experiments, including examples of clean and poisoned samples, as well as benign and malicious behavior at inference time. (a)DoS pretraining backdoor experiments. Credit: arXiv (2025). DOI: 10.48550/arxiv.2510.07192

Large language models (LLMs), which power sophisticated AI chatbots, are more vulnerable than previously thought. According to research by Anthropic, the UK AI Security Institute and the Alan Turing Institute, it only takes 250 malicious documents to compromise even the largest models.

The vast majority of data used to train LLMs is scraped from the public internet. While this helps them to build knowledge and generate natural responses, it also puts them at risk from data poisoning attacks. It had been thought that as models grew, the risk was minimized because the percentage of poisoned data had to remain the same. In other words, it would need massive amounts of data to corrupt the largest models. But in this study, which is published on the arXiv preprint server, researchers showed that an attacker only needs a small number of poisoned documents to potentially wreak havoc.

To assess the ease of compromising large AI models, the researchers built several LLMs from scratch, ranging from small systems (600 million parameters) to very large (13 billion parameters). Each model was trained on vast amounts of clean public data, but the team inserted a fixed number of malicious files (100 to 500) into each one.

Next, the team tried to foil these attacks by changing how the bad files were organized or when they were introduced in the training. Then they repeated the attacks during each model’s last training step, the fine-tuning phase.

What they found was that for an attack to be successful, size doesn’t matter at all. As few as 250 malicious documents were enough to install a secret backdoor (a hidden trigger that makes the AI perform a harmful action) in every single model tested. This was even true on the largest models that had been trained on 20 times more clean data than the smallest ones. Adding huge amounts of clean data did not dilute the malware or stop an attack.

Build stronger defenses

Given that it doesn’t take much for an to compromise a model, the study authors are calling on the AI community and developers to take action sooner rather than later. They stress that the priorities should be making models safer, not just building them bigger.

“Our results suggest that injecting backdoors through data poisoning may be easier for large models than previously believed, as the number of poisons required does not scale up with model size—highlighting the need for more research on defenses to mitigate this risk in future models,” commented the researchers in their paper.

Written for you by our author Paul Arnold, edited by Gaby Clark, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive.
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More information:
Alexandra Souly et al, Poisoning Attacks on LLMs Require a Near-constant Number of Poison Samples, arXiv (2025). DOI: 10.48550/arxiv.2510.07192

Journal information:
arXiv


© 2025 Science X Network

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Size doesn’t matter: Just a small number of malicious files can corrupt LLMs of any size (2025, October 10)
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Russia Wants This Mega Missile to Intimidate the West, but It Keeps Crashing

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Russia Wants This Mega Missile to Intimidate the West, but It Keeps Crashing


A Russian intercontinental ballistic missile (ICBM) fired from an underground silo on the country’s southern steppe Friday on a scheduled test to deliver a dummy warhead to a remote impact zone nearly 4,000 miles away. The missile didn’t even make it 4,000 feet.

Russia’s military has been silent on the accident, but the missile’s crash was seen and heard for miles around the Dombarovsky air base in Orenburg Oblast near the Russian-Kazakh border.

A video posted by the Russian blog site MilitaryRussia.ru on Telegram and widely shared on other social media platforms showed the missile veering off course immediately after launch before cartwheeling upside down, losing power, and then crashing a short distance from the launch site. The missile ejected a component before it hit the ground, perhaps as part of a payload salvage sequence, according to Pavel Podvig, a senior researcher at the United Nations Institute for Disarmament Research in Geneva.

The crash was accompanied by a fireball and a noxious reddish-brown cloud, the telltale sign of a toxic mix of hydrazine and nitrogen tetroxide used to fuel Russia’s most powerful ICBMs. Satellite images taken since Friday show a crater and burn scar near the missile silo.

Analysts say the circumstances of the launch suggest it was likely a test of Russia’s RS-28 Sarmat missile, a weapon designed to reach targets more than 11,000 miles (18,000 kilometers) away, making it the world’s longest-range missile.

An Unusable Weapon

The Sarmat missile is Russia’s next-generation heavy-duty ICBM, capable of carrying a payload of up to 10 large nuclear warheads, a combination of warheads and countermeasures, or hypersonic boost-glide vehicles, according to the Center for Strategic and International Studies. Simply put, the Sarmat is a doomsday weapon designed for use in an all-out nuclear war between Russia and the United States.

Therefore, it’s no wonder Russian officials like to talk up Sarmat’s capabilities. Russian president Vladimir Putin has called Sarmat a “truly unique weapon” that will “provide food for thought for those who, in the heat of frenzied aggressive rhetoric, try to threaten our country.” Dmitry Rogozin, then the head of Russia’s space agency, called the Sarmat missile a “superweapon” after its first test flight in 2022.

So far, what’s unique about the Sarmat missile is its propensity for failure. The missile’s first full-scale test flight in 2022 apparently went well, but the program has suffered a string of consecutive failures since then, most notably a catastrophic explosion last year that destroyed the Sarmat missile’s underground silo in northern Russia.



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Bryan Johnson Has Discovered Shrooms, and He Really Wants You to Know It

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Bryan Johnson Has Discovered Shrooms, and He Really Wants You to Know It


“Come watch me trip balls,” declared Bryan Johnson, the “Don’t Die” longevity entrepreneur, on X a couple of days before he livestreamed himself consuming a high dose of psychedelic mushrooms at a psilocybin center in Oregon on Sunday.

It marked the second act of his stunty new investigation into whether using psilocybin can improve almost 250 wellness biomarkers, including various measures of brain connectivity, cortisol levels, and testosterone.

“There’s a potential for psychedelics to play a more important role in all of our lives, and wouldn’t it be amazing if it was also a longevity therapy,” Johnson proclaimed on the stream. Prior to consuming the shrooms Sunday—which has been legal at licensed facilities in Oregon since 2023—Johnson measured his brain activity with a $50,000 helmet produced by Kernel, a neuroimaging company founded by the 48-year-old. He also took saliva samples and temperature readings. (After his November trip, he shared a lot of information about the state of his erections, but more on that later.)

Then he drank more than five grams of powdered mushrooms mixed with lemon juice, for extra potency. Johnson grimaced, and a bizarre new era of live celebrity psychedelic exhibitionism was born—one that is arguably counter to the introspective nature of the drug. The five-and-a-half-hour livestream, which has been viewed more than 1.1 million times, also featured Johnson’s 20-year-old son Talmage, whose blood he has injected in his efforts to stay young, journalist Ashlee Vance, a DJ set from Grimes, and Salesforce CEO Mark Benioff. YouTuber MrBeast, while pictured on a cartoonish poster advertising the event, did not show up, which most extremely high people would probably count as a blessing.

Observers noted that livestreaming an intense psychedelic trip might not be beneficial, since it can lead to fragmented attention and performance stress. Johnson appeared to acknowledge this before taking the mushrooms, saying, “I guess the biggest question is, can I not go off the rails?”

“Having the whole world being able to watch you may not facilitate the best outcome,” says Rayyan Zafar, a postdoctoral fellow at the Centre for Psychedelic Research and Neuropsychopharmacology at Imperial College London. “Bryan’s setup speaks more to ego enrichment than ego dissolution and is characteristic of many of his pseudoscientific pursuits. These sorts of experiences are often best held with an introspective and internal focus.” (Ego death, where one’s sense of self dissolves, is an experience some people seek when taking various psychedelics.) Jamie Wheal, the author of Recapture the Rapture: Rethinking God, Sex, and Death in a World That’s Lost Its Mind, was more brutal in his assessment, telling WIRED the project is “a circus of self-indulgence” and an exercise in “digital narcissism.” He asked: “Is this the psychedelic renaissance that all the supposed freedom fighters and prisoners of conscience have been stumping for?” (Asked if he would like to respond to critiques of his methods, Johnson told WIRED: “Whoever said this, I wish them well.”)

But while someone tripping balls on camera might seem performative and not particularly riveting—at one point Johnson plays with a slinky after declaring “everything is alive”—his broadcast could also help reduce stigma around drug use. “I think it’s fine and good to show people what the experience [of taking psychedelics] looks like, to demystify it to some extent, to show that it can be beneficial,” said journalist and psychedelics industry consultant Hamilton Morris on the livestream; Morris hosted the Vice show Hamilton’s Pharmacopoeia, which depicted him doing drugs on camera.



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HBO Max’s ‘Mad Men’ Vomit Scene Proves ‘Remastered’ Doesn’t Mean ‘Better’

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HBO Max’s ‘Mad Men’ Vomit Scene Proves ‘Remastered’ Doesn’t Mean ‘Better’


But the problem goes beyond a change of aspect ratio. Remastering shows that were originally shot with more primitive technology sometimes goes horribly awry, like an I Love Lucy clip that went viral last year showing a pair of once-blurry background actors brought into so much focus that they now looked like surreal Picasso sketches.

I visited the set of Frasier in the late ’90s, as the TV industry was preparing for the shift from standard to hi-def. As I admired the decor of Dr. Crane’s living room, one of the acclaimed sitcom’s producers lamented that all of it would look much shabbier in HD than in the more visually forgiving SD format, and worried that they’d have to go to the expense of rebuilding all of their standing sets. Frasier, Lucy, and so many others were created without a thought to how they might one day look in a format that didn’t exist at the time.

While countless classic movies have been successfully remastered for HD or 4K, they’re also stand-alone projects, where real care and attention can be given to each frame. Seinfeld and I Love Lucy both made 180 episodes. The Simpsons made 429 episodes in standard-def. Doing quality control with that amount of product is very difficult, which is how so many of these mistakes get made. (In the case of The Simpsons, Disney+ eventually introduced an option to watch the first 20 seasons in their original aspect ratio.) Every now and then you get a situation like The Wire, whose creator David Simon insisted on being involved in the process of changing the gritty urban drama’s image quality and aspect ratio, but it’s rare.

This specific Mad Men error is an odd one, since the show was always presented in HD widescreen. But the first four seasons were shot on film, so perhaps in the remastering process, someone inadvertently used an alternate take of the vomit scene where the crew members hadn’t been digitally erased. A source close to the process said that Lionsgate gave HBO Max “incorrect files” and that the proper versions will be uploaded ASAP.



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