Microsoft has recently released the April updates for the Outlook 2010/2013 Junk E-mail Filter.
"This update provides the Junk E-mail Filter in Microsoft Office Outlook with a more current definition of which e-mail messages should be considered junk e-mail."
The update is available for Outlook 2010 (32-bit, 64-bit) and Outlook 2013 (32-bit, 64-bit) or you can use Microsoft Update. As usual the update comes with the corresponding Knowledge Base article: