O Chrome 25 está adicionando dois novos recursos para impedir instalações de extensões silenciosas. Da postagem no blog do Chrome :
Extensions installed by third party programs using external extension deployment options will be disabled by default. When a third party program installs an extension, the Chrome menu will be badged, and users can click through the Chrome menu to see a dialog containing an option to enable the extension or to remove it from their computer.
In addition, all extensions previously installed using external deployment options will be automatically disabled. Chrome will show a one-time prompt to allow the re-enabling of any of the extensions.
Não sei se isso bloqueará todos os hijacks de mecanismos de pesquisa, mas ajudará muito a interromper muitos deles.