In mission 6A, "Piercing Encounters," when you fight the Borg, let them assimilate the Typhon. Your mission will fail (obviously). Then, choose to not restart the mission. Your debriefing will then come up and it will show Borg machines. Just sit there, and eventually, the Borg machines will take over a large part of your screen.
Level select
At the level selection screen, press Up, Left, Down, Right, Up, Right, Up, Down, Left, Up, L1 + R1, L2 + R2 to unlock all levels.
Secret mission 1A
Successfully complete mission 1 in under 5 minutes 2 seconds with more than 40% accuracy.
Secret mission 4A
Successfully complete mission 4 in under 6 minutes 44 seconds with more than 40% accuracy.
Secret mission 5A
Destroy half of the energy plough and use your tractor beam on the second half in mission 5.
Secret mission 5B
Search for the info unit between the two asteroids, near the broken shuttle in mission 5 and use the tractor beam to acquire it.
View credits
At the mission briefing screen, press [Left, Right, Up, Down] five times.