title: Random text masking in c#
body: <p>What is the best way to mask 3 random letters in a 5 letter word in c#?
  For example, if input string is "12345" then I need to convert it to one of the following outputs.
  "12***" or "1*3**" or "1<strong>4*" or "*23</strong>" or "*2*4*" or "*2**5" or "**34*" or "**3*5" or "***45"</p>
  
  <p>Thanks!</p>