I just want to ask if Ultrasurf can cause network to go down?!
I was just going to install Ultrasurf to test it out and found it's infected with malware. Whether these are false positives or not, I'm not sure (the community seems to be at a consensus that it's malicious) so I'm not going to proceed.
However, ANY vpn will probably cause your network to go out momentarily while it switches from your default connection to the VPN, same for disconnecting and going back to your default connection.
I assume you're going to use this in your school. It won't effect the entire network, only the system that it's installed on, unless the system you install it on acts as a host to the clients in the network. Most competent school IT staff won't allow program installations anyway.