gistfile1.txt

public class SecureTransactor
{
  public bool DoManySecureTransactions(string[] data)
  {
    if (!SecurityCheck()) return false;

    bool doCheck = false;   // We already did the check, no need to repeat ourselves!
    foreach(string datum in data)
    {
      InternalDoSecureTranaction(data, doCheck);
    }
  }
  
  public bool DoSecureTransaction(string data)
  {
    bool doCheck = true;
    return InternalDoSecureTransactions(data, doCheck);
  }
  
  protected bool InternalDoSecureTransaction(string data, bool doSecurityCheck=true)
  {
    if (doSecurityChecks && !SecurityCheck())
      {
        return false;
      }

      // ...

      return true;
  }

  protected bool SecurityCheck()
  {
    // ...
  }
}