Alerts from your anti virus software flagging Arc.exe (Arc for Windows) as a virus or trojan are very likely a false positive. We've run Arc.exe through Virus Total with clean results.
We're working with the major anti virus software providers for Windows to get Arc.exe on their whitelists to prevent these false positives from occurring.
In the meantime you can add Arc.exe to your anti virus software's list of trusted applications. Check your anti virus software's support documentation for instructions on how to do this.
If you have additional questions about the security of Arc for Windows contact us: security@thebrowser.company.