This indicates an attempt to exploit a buffer overflow vulnerability in Yahoo! Toolbar.
The vulnerability is caused by boundary errors within the YShortcut ActiveX control component of Yahoo! Toolbar. A remote attacker can exploit this vulnerability by enticing the target user to open a crafted webpage, potentially causing arbitrary code to be injected and executed in the security context of the current user.
Yahoo! Toolbar 1.4.1
Currently we are not aware of any vendor supplied patch for this issue.