Edit: Per comments below. It would seem that the Outbreak of crime period does not occur if you play a custom game with low intensity. If you are looking to make the Outbreak of crime period happen in a custom game, choose moderate intensity of higher.
This achievement is unlocked for getting through the "Outbreak of crime period"
without being robbed while being raided. This period happens randomly in the game so you cant really dictate when its going to come about, you can only prepare for it and deal with it when it happens.Note: Getting raided and having things stolen before the outbreak of crime period will not affect this achievement.
A few pointers to consider with this achievement:
When you upgrade your workshop to level 2, there is a board up construction option than can be constructed up to three times. This construction option helps with reducing the frequency of when you are raided. I would suggest getting this early on as it helps when outside the outbreak of crime period.
Have 2 people on guard at night, also a must for the outbreak of crime period. This will leave you with a greater chance of not being robbed when raided. Having 2 people on guard duty will also unlock the following achievement:
Having weapons and armor in your stockpile affect how well your guarding / in base characters defend themselves when being raided. This relates to whether you are robbed when raided as well as characters being injured or not from the raid. Shovels and crowbars count as weapons and are a great option for early game base defense.
In short, you know this period is going to happen at some stage during the game. So you must be prepared for when it hits.