An ISIL propaganda song was played on one of Sweden’s most popular radio stations for about 30 minutes on Friday morning.
The owners of Mix Megapol said the station’s frequency was hacked to play an English language pop song, urging people to join the extremist group.
The propaganda song called For The Sake Of Allah was played on the internet-based radio station in Malmo, according to local news website 24 Malmo.
Jakob Gravestam, a spokesman for parent company Bauer Media, said the incident had been reported by listeners of the show.
"A lot of people have called us about this. We are very happy that people are vigilant and we treat this very seriously," he told 24 Malmo.
While Jonas Wessel from Sweden's Post and Telecoms agency said it was unlikely the hackers would ever be found.
"It seems like someone has used a transmitter and dialled the same broadcast frequency and then played out different content,” Mr Wessel told the Aftonbladet newspaper.
"Afterwards it is very difficult. If it is a disturbance that only occurs during a period and never occurs again, it is difficult to find."
The radio station has reported the incident to the police to investigate.