When does F-Secure notify you of the suspected virus? During the download, during a scan, or during the installation? Sometimes antivirus software gets a little aggressive about reporting viruses during the course of program installation, since files are "changed" during software installs.

I've scanned the downloaded file (en_fishtycoon_inst from Big Fish Games) with the latest Norton AntiVirus and found nothing amiss. Is it possible that you're seeing a false positive?