There are many web sites outlining how to reconfigure windows XP, Vista, and Windows 7 to allow multiple concurrent Remote Desktop Sessions, basically making a desktop PC a terminal server. On many occasions I have pointed out doing so is a licensing violation, however I confess I have never seen this specifically stated in any ELUA. I have been privy to discussions with Microsoft where this has been discussed, and Microsoft employees and support site personnel have often posted it is not permitted on various sites.
Having been asked to verify this I reviewed various EULAs (End User Licensing Agreements) and it seems Microsoft more often explains in detail what is allowed than what us not. Much like your insurance company doesn’t state in your home owners policy you are not permitted to have bonfires in your basement. Some ELUAs such the one for Windows 7 mentions; “The single primary user of the licensed computer may access a session from any other device using Remote Desktop”, but does not state you can have multiple sessions. It does however state you can have multiple users sharing a single session using NetMeeting or Remote Assistance, which means both users are sharing the same desktop and application, not separate sessions. The intent with this is to assist an end user.
The modification is promoted as a patch, but a patch would be provided by Microsoft. This ‘patch’ was created by someone named DeepXW who on their own web page refers to it as “Crack termsrv.dll, remove the Concurrent Remote Desktop sessions limit”.
Most of the reputable sites explaining the hack also include a disclaimer explaining it is a violation. I have posted some examples at the end of my ramblings . Sites such as Experts-Exchange have even banned posting the hack as they have confirmed it is a licensing violation.
We also need to consider if this hack were legal, you would also require buying RDP/RDS CALs (Client Access Licenses), and if Office were installed you would only be legit if you purchased volume licensing with one license for each user. The latter two are requirements on any multi-session Microsoft O/S. The Office 2013 ELUA does clearly state that you cannot have multiple sessions: “Remote access. The user that primarily uses the licensed computer is the “primary user.” The primary user may access and use the software installed on the licensed device remotely from any other device, as long as the software installed on the licensed device is not being used non-remotely by another user simultaneously.” This same issue applies to third party software which in many cases has the same limitations.
Granted the hack does work, with some occasional Winsock issues, and though the chances of being caught are minimal, if discovered in a Microsoft audit, which does happen, the penalties are stiff. I strongly encourage folk to approach this in a more secure, manageable, and legitimate way by using a Microsoft Remote Desktop Services Server (formerly called Terminal server).
Sample comments from various sites outlining the hack:
However, be warned. Before you begin, I need to warn you that patching the file and allowing more than one concurrent Remote Desktop session will violate a few lines in the Windows XP EULA. Proceed with caution and at your own risk. I shall not be liable for any damage caused to you, your computer, your data or your dog/cat because of this. From <http://www.petri.co.il/multiple-remote-desktop-sessions-on-windows-xp-sp3.htm>
Desktop, which basically only allows the single primary user of the licensed computer to access a session of the computer. And that essentially tells us that the trick we revealed to enable multiple concurrent user in remote desktop in Windows 7 isn’t a legally licensed, despite that it’s really a good useful hack. From <http://www.nextofwindows.com/how-many-concurrent-connections-allowed-to-access-a-windows-7-computer/
I think you find it is a license violation, as win 7 is single user at time OS.
As with all version of windows you need a license for all current users.
If you “hack it” you have violated the TOS and have voided the windows license. From <http://social.technet.microsoft.com/Forums/windows/en-US/41e9e500-714a-443b-bff2-55f0d500d3d1/concurrent-sessions-remote-desktop-in-windows-7>
A quick note: enabling multiple concurrent RDP users may be against the Windows 7 End User Licensing Agreement (EULA). Please be sure to check the EULA beforehand and know that we do not recommend making these changes in cases where they may violate the EULA. From <http://www.optimusbi.com/2012/12/05/enable-concurrent-rdp-connections-windows/>
Regardless of what solution you come up with, concurrent desktop access (if you are not sharing a single session) is in violation of the desktop Windows EULA. From <http://arstechnica.com/civis/viewtopic.php?f=15&t=1190558
LAN-Tech Network Management 
Comments on: "Multiple RDP Sessions on a PC –legal or not" (7)
Thanks for information. I have thought the same way. I have problem with one other thing. While I think we agree on violating tos via concurrent sessions what about following situation:
Family or Small business has 1 windows pc with 1 MS Office used by multiple users. They do not work concurrently. In your post is mentioned that primary user can use the system and its sw remotely as long as no-one else is using remote computer (1 user at a time). Non-server Windows editions in general, without hacking work this way but my question relates to this:
If we have 3 users using the machine the same amount of time for the same purpose – ms office, can they remote to that machine and use it as if they would be using it locally? I mean One user at a time.
Yes, you can have as many users as you like logging in locally or remotely so long as only one at a time. Only Windows pro versions support remote access and a new user can only log in if the previous user logged out, or they are an administrator, which can “bump” a user.
Thank you! That’s what I needed to hear. Now I just need to get confirmed how it is with connecting to pc to use MS Office 2013 Professional because I have read that you are not allowed to use any version of ms office remotely (I think only Professional plus but I might be wrong)
I have never heard that or read in Microsoft licensing. If you have a terminal server you need to have Office enterprise, but a workstation does not require that as it is one user at a time.
There are companies such as Aikotech ThinServer and Thinsoftc Winconnect which enable terminal server on desktop OS without hacking the dll file
One would assume they are legal but technically they are in violation of the Microsoft licensing agreement on multiple levels.
[…] This link states that it would not be legal because a single-user license would be used by multiple users. But is it technically possible, and can we register a license for every user to keep it legal? […]