The court sentenced the 32 year-old defendant to 9.5 years in prison for convictions on one count of aggravated child sexual abuse, 29 counts of child sexual abuse and three counts of sexual abuse.
Petri Joonas Ylönen has been in prison since April 2015 and remained in detention during his court hearing.
The court heard that the man used different online discussion forums to befriend young girls under the age of 16.
The defendant’s sentence also reflected convictions for six counts of distributing indecent sexual images and 25 counts of possession of indecent sexual images of children.
The man was also ordered to pay a total of 98,000 euros compensation to 28 plaintiffs for suffering he caused them.
A psychiatric evaluation found that the man was criminally responsible for his actions.