Drupal 7 - Custom block hooks

custom_block.php

<?php
/**
 * Implements hook_block_info().
 */
function YOUR_MODULE_block_info() {
  $blocks = array();

  $blocks['YOUR_BLOCK_ABC'] = array(
    'info' => t('YOUR BLOCK NAME'),
  );

  return $blocks;
}

/**
 * Implements hook_block_view().
 */
function YOUR_MODULE_block_view($delta = '') {
  $block = array();

  switch ($delta) {
    case 'YOUR_BLOCK_ABC':
      $block['subject'] = '';
      $block['content'] = _YOUR_MODULE_BLOCK_ABC_CONTENT();
      break;
  }

  return $block;
}

function _YOUR_MODULE_BLOCK_ABC_CONTENT() {
  $output = t('Hello world');
  return $output;
}