Signal has rapidly gained in popularity as Silicon Valley monopolists have grown more openly hostile to free speech, but the platform may be vulnerable to backdoors that undermine the privacy protections provided through the encrypted messaging service.According to documents filed by the Department of Justice and first obtained by Forbes, Signal's encrypted messages can be intercepted from iPhone devices when those Apple devices are in a mode called  "partial AFU," which means "after first unlock."

When phones are in partial AFU mode, Signal messages can be seized by federal authorities and other potentially hostile interests. GrayKey and Cellebrite are the tools typically used by the FBI to gain this sensitive information, an expert has explained.