1. A method comprising: operating a web server to receive a call to an anti-injection client-side code from a web browser, wherein the call is facilitated by a code segment in a web page loaded by the web browser; transmitting the anti-injection client-side code from the web server to the web browser, wherein the anti-injection client-side code comprises instructions which, when executed: (i) in a main execution thread of the web browser, intercept an injection of a node into the DOM (Document Object Model) of the web page, (ii) in a web worker execution thread of the web browser, compare the injected node with a list, by performing any of: (a) employing a regular expression (RegEx) to identify a string of characters in the injected node, based on information contained in the list, (b) observing changes to the DOM by a MutationObserver application programming interface (API) of the web browser, or (c) overriding an API of the web browser, wherein the API is selected from the group consisting of: appendChild and insertBefore, and (iii) in the main execution thread of the web browser, based on the comparison, permit or block execution of the injected node in the web browser; and defining, in the code segment, that the anti-injection client-side code be loaded by the web browser synchronously, to prevent the web browser from loading the injected node before the anti-injection client-side code is executed, wherein the definition in the code segment comprises an “async” attribute that equals “false”.