Lyric discussion by booyay 

The Trojans metaphor isn't referring to a condom or the Trojan horse from greet mythology.

Going by the rest of the song it seems to be referring to a trojan virus. All the thoughts/memories are looked at as files on a computer. A trojan virus is usually attached to file you download and once in your computer spreads and corrupts the whole system.You can delete the original file it came with, but once the trojan is there it's near impossible to get rid of without rebooting your entire system.

Using that metaphor the song seems to be about trying to get over a past break up. You can try to change as much about your life to try and forget about a big relationship but a part of it will always be remembered. You can try changing the locks, or throwing out old photos but the relationship (virus) will always be there.

Isn't the Trojan virus named after the Trojan horse though? Because of the similar nature of the problem, not being able to get it out.

Your analysis seems to be the most accurate, but I do agree that it's ok to assume they mean either the Trojan Horse or Trojan virus because both sneak in and destroy from the inside out, much like a great relationship gone wrong can feel.

I disagree, it could refer to a planet/moon defined as a trojan en.wikipedia.org/wiki/Trojan_%28astronomy%29.....which would fit with the songs overall theme of being preoccupied with and daydreaming about the song's love interest. Also, it makes much more sense than any other commonly used definition of the word trojan...

An error occured.