Artistic group Ztohoven broke via the internet into a camera / camera server which provided images from the Krkonose Mountains as part of the morning panorama program. They fed a 30 second film which showed images of an atomic explosion and the group's web address. According to initial investigations by the Czech authorities, the CT2 network itself was not affected, the compromised camera server was operated by an outside contractor.
CT2 has reported the matter to the police, and should someone be successfully prosecuted, a one year prison sentence could be imposed.
English links here and here, lot's of coverage in Czech media media"