This can be used by malicious or erroneous Tclets to mount resource attacks, to cause the hosting applications to run out of network resources or file descriptors. When this happens, no other sub-system running in the hosting application will be able to make network connections using sockets. In the Tcl plugin, if the Tclet is executing in an external process and not in the address space of the hosting browser, only the external process runs out of network resources, while the hosting browser continues to be able to connect to remote sites. See the plugin manual entry for more details. A socket can be maliciously or mistakenly be put into blocking mode, by using the fconfigure command.
Sockets are in blocking mode when they are first opened with the socket command.
If the Tclet tries to read from the socket when there is no input available, or if it tries to write when the output buffer is full, the Tclet can block the entire hosting application. In the Tcl plugin, if a Tclet is executing in an external process and not in the address space of the hosting browser, only the external process is blocked and the browser continues to function normally. Thus this only affects other Tclets that may be executing at the same time. Another risk incurred by the network feature is a risk to your reputation. If you allow a Tclet to connect to the SMTP or NNTP services on any host, the Tclet can forge news articles or send electronic mail using your name.