AOL 9.0 Security Edition revision 4184.2340, and probably other versions, uses insecure permissions (Everyone/Full Control) for the "America Online 9.0" directory, which allows local users to gain privileges by replacing critical files.
AOL Client Software 9.0 uses insecure permissions for its installation path, which allows local users to execute arbitrary code with SYSTEM privileges by replacing ACSD.exe with a malicious program.