The hepatitis B virus (HBV) is responsible for one of the most serious and common infectious diseases. Transmitted through biological fluids, it attacks the liver cells. The chronic form of the disease can lead to serious complications, including cirrhosis and liver cancer. There is no effective treatment for the chronic form of the disease, which can only be prevented by vaccination. After identifying a key protein complex that is active when our body is infected by the virus, a team has deciphered the precise functioning of this protective mechanism, opening the way to new therapeutic targets.