Magento Custom Multi Select Customer Attribute

Version: Magento 1.x

Problem:
Create a simple custom multi select customer attribute programmatically via upgrade script.

Solution:

$attributeCode = 'my_attribute';
$installer->addAttribute('customer', $attributeCode, array(
    'type' => 'varchar',
    'label' => 'My Attribute',
    'input' => 'multiselect',
    'source' => 'eav/entity_attribute_source_table',
    'backend' => '',
    'visible' => false,
    'required' => false,
    'unique' => false,
    'option' => array (
        'value' => array(
            'Option1' => array('Option1'),
            'Option2' => array('Option2')
        )
    )
));

$attribute = Mage::getSingleton('eav/config')
    ->getAttribute('customer', $attributeCode);
$attribute
    ->setData('used_in_forms', array('customer_account_edit'))
    ->setData('is_used_for_customer_segment', true)
    ->setData('is_system', false)
    ->setData('is_user_defined', true)
    ->setData('is_visible', false)
    ->setData('sort_order', 100);
$attribute->save();