PARIS (AP) — French researchers have released software tools that they claim can restore some of the computers locked up by a global cyberattack that held users' files for ransom.

The researchers said, however, that the tools are not perfect and work only if the computers infected with the WannaCry ransomware have not been rebooted after being hit. For that reason, the technique isn't likely to help many people. In addition, companies needing to restore their operations right away likely would have turned to backups, if available, by now.

The developments came Friday, the apparent deadline for...