Scanned a local Ubuntu Linux and Windows 7 Pro system. Scan shows port 80 open/listening?
Run netstat -plnt locally and port 80 not open. False positive? Why?
It's unlikely to be a false positive. As far as I can tell if a port is reported open, the NetScan was able to make a connection.
Try telnet x.x.x.x 80 to the IP addresses in question. If it prints an error, then something appears to be wrong with NetScan. Otherwise the port is indeed open.