Packet Tracer is provided by Cisco for learners who participate in Cisco Networking Academy courses; Cisco makes downloads available to students and instructors through the Networking Academy site. There are also official distribution channels for community learners. To obtain a legitimate copy:
Cisco Packet Tracer version 8.1.1 is available as a "previous version" for users with specific compatibility needs, though Cisco strongly recommends using the latest release (version 9.0.0).