"Helsinki syndrome" is a misnomer for Stockholm syndrome. Stockholm syndrome is a psychological disorder in which people who are abused or held captive start to identify with and care for their abusers or captors.
Stockholm syndrome occurs when a person is held captive or seriously abused. The person becomes so used to this treatment and behavior that, as time progresses, the victim begins to identify the captor as a friend rather than an enemy. The abused person begins to have positive feelings toward the criminal and views the police, friends and family as enemies. Well-known incidents in which people suffered from Stockholm syndrome are the Patty Hearst case and the Elizabeth Smart case. The syndrome was erroneously referred to as "Helsinki syndrome" in the first "Die Hard" movie, and the misnomer continues to appear in popular media.