Anthropic says it has blocked several attempts to misuse its Claude artificial intelligence models for activities that could support the development of biological weapons.
The AI company revealed the cases in its latest threat intelligence report, which covers suspected misuse of its models between December 2025 and August 2026. The report details how AI was used or tested for a range of harmful activities, including biological research, weapons development, cyberattacks, surveillance, scams and propaganda.
Anthropic said it identified five cases involving biological research that could have supported the development of biological weapons. The company said these cases show how more capable AI models are creating new safety challenges because the same scientific knowledge can be used for both legitimate research and harmful purposes.
Anthropic Identifies Five Biological Misuse Cases
Anthropic described biological misuse as one of the most serious risks linked to advanced AI. The company said AI can help researchers with tasks such as finding scientific information, analysing data and planning experiments. While these abilities can support medical research and the development of treatments, they could also be misused to support dangerous biological work.
Anthropic said it detected five cases where users were using its models in ways that could contribute to biological weapons development. The company investigated the activity and took steps to block or restrict the accounts involved.
However, Anthropic stressed that the cases did not necessarily involve people openly asking AI to create a biological weapon. Jacob Klein, Anthropic’s head of threat intelligence, told The New York Times that the situation is more complicated than a user simply asking an AI system how to build a weapon.
Users can divide their work into smaller requests that appear harmless on their own. This can make it difficult for AI companies to identify the user’s overall goal.
AI’s Scientific Abilities Create a Safety Challenge
Anthropic said the growing scientific capabilities of AI models are making biological safety more difficult. The company said the same information that could be used to develop a biological weapon could also help scientists develop vaccines or treatments for diseases.
This creates a difficult balance for AI companies. They need to allow researchers to use AI for legitimate scientific work while preventing the technology from providing assistance that could cause serious harm.
Anthropic said its experience shows that simply blocking individual prompts may not be enough. AI companies may also need to look at patterns of activity and other warning signs when deciding whether an account is being used for harmful purposes.
Claude Was Also Used in Other Weapons-Related Activity
The report found that Claude was also used in attempts to support the development of conventional weapons. Anthropic identified six cases involving software related to firearms, missiles, armed drones, bombs and other weapons. Some of the activity also involved systems used for targeting and controlling weapons.
The company said it disrupted these activities and used the information gathered from the cases to strengthen its safety systems.
AI Misuse Is Growing Beyond Weapons
Anthropic’s report also identified cases involving cybercrime, surveillance, scams, fraud and influence operations. The company said cybercriminals and state-backed groups are increasingly using AI to support their activities.
In one case, a group linked to Russia allegedly used AI to develop malware that could identify when its code had been detected by security systems and then change the code to avoid detection.
Anthropic also said Claude had been used by actors connected to a Russia-based cyber espionage campaign and an Iranian propaganda organisation. The company said it blocked accounts involved in harmful activity and shared information with government agencies and industry partners where appropriate.
Anthropic Says Stronger AI Safeguards Are Needed
Anthropic’s report comes as concerns about advanced AI systems continue to grow. As AI models become better at scientific research, coding and other complex tasks, they can become more useful to researchers and businesses. At the same time, the same capabilities could make it easier for criminals or other harmful actors to use AI for dangerous activities.
Anthropic said it has used the findings from its investigations to improve its systems for preventing, detecting and stopping misuse. The company said it will continue working with governments and other technology companies to identify emerging threats and strengthen safeguards as AI systems become more capable.
The latest cases do not mean that Claude was used to successfully create a biological weapon. Instead, Anthropic says they show how advanced AI could increasingly be used to support activities that pose serious risks if stronger safeguards are not put in place.