The author of Greasemonkey and a group of developers working with him have found that rogue web pages that happen to know you are running Greasemonkey (far and few between at this point I'm sure) can execute the GM-specific functions (trusted JS) by the pages the GM scripts are running on themselves. So please, UNINSTALL the Greasemonkey extension, and install the version located at the bottom of this page instead: http://mozdev.org/pipermail/greasemonkey/2005-July/004032.html
This is a version of greasemonkey that has many of the useful and great greasemonkey specific features disabled until a further security update is made to the extension itself.