1. A computer-implemented method comprising: identifying a program binary file as part of content of a webpage accessible to a client computing device through a network, wherein the program binary file contains compiled instructions that run natively on a computing machine and is offered for downloading from the webpage to the client computing device for execution by the client computing device; analyzing the program binary file, the analyzing including identifying a tainted variable in source code associated with a browser-executable web application or browser extension that is installable on a client computing device as a consequence of executing the program binary file by the client computing device; re-writing the source code of the browser-executable web application or browser extension to include information to track a flow of the tainted variable during execution of the re-written browser-executable web application or browser extension; executing the re-written browser-executable web application or browser extension in a browser run by one or more processors; automatically determining, by the one or more processors, based on evaluation of results of executing the re-written browser-executable web application or browser extension whether the browser-executable web application or browser extension violates one or more predetermined conditions; and based on the determination, automatically determining whether to discourage downloading the program binary file from the webpage to the client computing device or whether to disable execution of the browser-executable web application or browser extension on one or more client computing devices.