Malware Detected on OpenTTD by Windows Defender

That's what's known as a false positive. We have a section on it on our Support page right here: https://portableapps.com/support#false_positive

AntiVirus engines are wrong all the time. Whenever you get an alert like that, you can double check it with VirusTotal.com which is run by Google. VirusTotal shows you the results of dozens of antivirus engines scanning that file. In this particular case, it looks like openttd.exe is detected by Microsoft's Windows Defender, so let's check that:

https://virustotal.com/en/file/6fc6db7dececfcbf6e2e6cf483e89da913cd9c586...

From the list, you'll see that while a couple smaller engines have a false positive, everything else both big and small show it correctly as clean. Kaspersky, McAfee, Symantec, Comodo, etc... all clean. Note that Microsoft's antivirus engine is not included in the results as I don't think Microsoft participates in the initiative anymore, which is a shame.

The file in question is part of OpenTTD's main package and is unaltered by us. It was, however, scanned by us before we packaged it and released it. We scan all our apps with at least two major antivirus engines before release, something no other portable software site does.