That antivirus is bugged, and has got a false positive. We digitally signed our files and we use an additional digital signature with the industry-standard Taggant system, which should help the antivirus not mistakenly flag a legit program as a threat.
Unfortunately, not all antivirus supports this standard, so they still make mistakes.
Download and install with the antivirus disabled. And configure it to exclude the whole FSX folder from scanning before starting FSX.
