Eric Romang discovered that gtkdiskfree, a GNOME program that shows free and used space on filesystems, creates a temporary file in an insecure fashion.
The old stable distribution (woody) does not contain the gtkdiskfree package.
For the stable distribution (sarge) this problem has been fixed in version 1.9.3-4sarge1.
For the unstable distribution (sid) this problem will be fixed soon.
We recommend that you upgrade your gtkdiskfree package.