In the past, the banner grabbing method was used to detect remote operating systems. Telnet Connect used to be sent to a targeted system and the system would display a banner of the operating system running on a host. This was not a very accurate method as the system admin could also disable a banner or change the actual banner in order to misguide attackers.
The new method of remote OS detection is to analyze the packet between the source and destination. This detection technique detects OS platforms and OS versions as well.
