This is why I'm very cautious in using any type of search engine toolbar (Google, Yahoo, etc).
Google is working to fix a bug in the Google Toolbar that could allow criminals to steal data or install malicious software on a system, a security researcher warned Tuesday.
The flaw lies in the mechanism Google Toolbar uses to add new buttons on the browser. Because the toolbar does not perform adequate checks when new buttons are being installed, a hacker could make his button appear as though it was being downloaded from a legitimate site when in fact it came from somewhere else.
More information can be found at InfoWorld.