When developing IPERF for Windows, we tried to keep it as simple as original Iperf one-file solution. So we embedded iperf.exe into GUI application. Modern antivirus systems, like Microsoft Forefront Endpoint Protection and others, don't like that. For example, Microsoft Windows Essentials brings up this message:

and shuts down IPERF. That's false positive alarm, there is no virus there. To prevent that behaviour, create the exception here:

To ensure that you have genuine IPERF for Windows, not modified with any malicious code, it is signed now with DigiCert certificate. Right-click the executable and in Properties check the 'Digital Signature' tab. In Windows 7 and 8 it looks similar: