Security researcher Long Zheng has posted notification (along with a proof of concept) of an issue in the beta version of Windows 7. He’s shown how an attacker could bypass the User Account Control (UAC), although he’s also shown how it can be remedied quite simply.
The UAC has been a bane of Vista users, as it notifies the user every time a program tries to alter the system. Many have disabled UAC because of its frequent dialog boxes. In Windows 7, though, Microsoft has granted new rules that allow changes to Windows settings without notification, although other alterations still requite notifying the user.
