Twitter now provides the more secure SSL option by default as noted below: 

Twitter – now offers SSL by default

QUOTE: Twitter has begun setting users to use HTTPS for all connections by default. Twitter PR announced this in a tweet recently which linked to a support document which explains more.  HTTPS, also known as SSL, authenticates the web site and encrypts all communications between the client and server. When used with plain-text HTTP, traffic from sites like Twitter can be monitored, even modified, by other users on the network.