Most characters have at a DeepDarkSecret or two. It's things that they don't want other characters to know about, for whatever reason. I'm going to share a small piece of advice here:

The easiest way to keep an IC secret is to keep it an OOC secret as well

There are several reasons for this, which I'll explain below:

1. Some people are just out and out cheaters. I don't believe that this is a problem in TreasureTrap?, but at any large LARP system, there will be a few. It's best to get into the habit of not spreading around your IC secrets OOC, as you won't get burned so easily when you go to a large system.
2. Some people have bad memories. If they get told something OOC in October, by January they may remember what it was, but not that they were told OOC.
3. Some people don't like knowing IC information OOC. If you know OOC that so-and-so is evil, it can really ruin the moment you find out IC. It can also put a dampener on your roleplay, as you avoid picking up on clues, because you aren't sure if you are acting based on the IC or OOC information available.