On the Windows Live team blog it is noted that Hotmail security has been improved to include optional full https sessions. This is part of a number of security updates to help enhance the protection level of Hotmail accounts. Next to this update all SkyDrive, Photos, Docs and Devices pages will use SSL encryption as well. Enabling your Hotmail account to use HTTPS can be done here: https://account.live.com/ManageSSL.
If HTTPS is turned on for Hotmail sessions certain connections from programs will not work: these include Outlook Hotmail Connector, Windows Live Mail (the followup to Outlook Express) and Windows Live for Windows Mobile / Symbian.
In the comments of the blog update on the Windows Live team blog it is noted that these security updates may have been triggered by the recent news that Facebook and Twitter fail basic security test: Hotmail got a bad grade there too (a D-) but not as bad as Facebook or Twitter (an F). Best security results were achieved by GMail and WordPress (with SSL) which scored an A.