Wow when did this start?
" Twitter About Tailored Suggestions " - https://support.twitter.com/articles/20169421#
I'm not sure people understand the ramifications of this, basically any website you go to where signing in via Twitter is an option they are going to be tracking you and how often you visit etc.
Is this the kind of service you want Twitter providing? (it just appeared pre-checked in my Twitter "Settings page" today).