Added an optional secret to the code generation and regenerated the first batch of invite codes.

.gitignore

 node_modules
-.DS_Store
\ No newline at end of file
+.DS_Store
+secret.txt
\ No newline at end of file

CodeGenerator.coffee

 shorthash = require 'shorthash'
 uuid = require 'uuid'
 fs = require 'fs'
+assert = require 'assert'
+
+#
+# Implementation of hash sieve algorithm that I read
+# about at http://www.shamasis.net/2009/09/fast-algorithm-to-find-unique-items-in-javascript-array/
+# in CoffeeScript with slightly more literate code :)
+#
+Array.prototype.unique = ->
+
+    hashSieve = {}
+    arrayOfUniqueValues = [];
+
+    for item in @
+    	hashSieve[item] = item
+
+    for item of hashSieve
+    	arrayOfUniqueValues.push item
+
+    return arrayOfUniqueValues
 
 class CodeGenerator
 
+	secret: ''
 	folder: null
 	folderExists: false
 
@@ -12,18 +32,28 @@ class CodeGenerator
 		# do not accidentally overwrite earlier ones
 		@folder = 'codes/' + Date.now()
 
+		if fs.existsSync('secret.txt')
+			@secret = fs.readFileSync 'secret.txt'
+
 	generateUniqueCodes: (numCodes) =>
 
 		codes = []
+		i = numCodes
 
-		while numCodes
-			uniqueCode = uuid.v4() + '-' + Date.now()
+		while i
+			uniqueCode = uuid.v4() + @secret + '-' + Date.now()
 			shortUniqueCode = shorthash.unique(uniqueCode)
 			codes.push shortUniqueCode
-			numCodes--
+			i--
+
+		codes = codes.unique()
+
+		# Just to make sure.
+		assert.equal codes.length, numCodes, 'All codes must be unique.'
 
 		return codes
 
+
 	generateUniqueCodesAndSaveToFile: (numCodes, fileNameToSaveTo) =>
 
 		codes = @generateUniqueCodes(numCodes)