[Puppy]

pawn Код:

stock randomString(strDest[], strLen = 10)
{
    while(strLen--)
        strDest[strLen] = random(2) ? (random(26) + (random(2) ? 'a' : 'A')) : (random(10) + '0');
}

Credits to Ryder~.

And for the timer:

pawn Код:

public OnPlayerConnect(playerid)
{
      PlayerKickTimer[playerid] = SetTimerEx("KickEx", 300*60, false, "i", playerid);
      RandomString(PlayerString[playerid], 10);
      new string[64];
      format(string, sizeof string, "Type the following string: %s", PlayerString[playerid]);
      ShowPlayerDialog(playerid, DIALOG_VERIFY, DIALOG_STYLE_INPUTTEXT, "String", string, "ok", "ok");

      return 1;
}

public OnDialogResponse(playerid, dialogid, response, listitem, inputtext[])
{
      if(dialogid == DIALOG_VERIFY && response)
      {
           if(strcmp(inputtext, PlayerString[playerid], true) != -1)
           {
                // correct
           }
           else KickEx(playerid);
      }
      return 1;
}