It can be detected even without looking at the user agent (as another user mentioned). They typically rely on the fact that the downloaded source code is being

It can be detected even without looking at the user agent (as another user mentioned). They typically rely on the fact that the downloaded source code is being executed as it is being downloaded so you can leave things like "sleep 5" and detect the delay in fetching from the client. The best thing to do is to download first and then execute. Also good installer scripts first define a function and then call the function at the very end of the script so that they don't half-execute some function in case the network connection is disrupted.