Occasionally an anti-virus utility reports a false alarm on Windows, when installing Synfire.
The file SynfirePro.exe is digitally signed by Cognitone and can not be tampered with without destroying the signature. If the signature is still there and valid, this proves the file wasn’t modified by a third party and is therefore virus free. You can check the signature on the file info box.
If you download Synfire from Cognitone, it is practically impossible for someone else to inject malicious code into the download while it's on its way.
It is likely that the iLok protection scheme may look suspicious to the anti-virus utility, triggering a false warning. This is nothing to worry about. The warning should go away after the virus database will eventually be updated.