From Halopedia, the Halo wiki
Not to be confused with Infiltration.
Infiltrate (1:48) starts with a low strings note, with drums playing background. High strings play and hold a note, but drums continue to play melody. The piece picks up the pace, and louder drums join in. It plays during the encounter where John-117 faces Kig-yar Snipers after Echo 51 crashed, up until the beginning of the "Quid Pro Quo" section of the level. The melody was reprised in the later track Halo Reborn.
Move On (1:57) starts with strings beginning to play the melody, which is in a minor key but has a hint of major in it. Choir also joins in, but strings and drums still keep the melody, which alternates between major and minor. This melody continues until the end. The piece plays near the end of the level when Kilo 23 destroys the two Type-52 Phantoms.
When the bass begins followed by the three percussive sounds, seven such percussion sets follow before the percussion suddenly becomes high-pitched and then returns to normal. This may be a 7 reference.