Set and Get Session variables in magento

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Magento has functionality to create new session variables. You can set it as following

/* Core Session */
Mage::getSingleton('core/session')->setYourVariable('data');
$Data = Mage::getSingleton('core/session')->getYourVariable();

/* Customer Session */
Mage::getSingleton('customer/session')->setYourVariable('data');
$Data = Mage::getSingleton('customer/session')->getYourVariable();

/* Admin Session */
Mage::getSingleton('admin/session')->setYourVariable('data');
$Data = Mage::getSingleton('admin/session')->getYourVariable();