I have a Twitter account set up for a blog I post to once a week or so. The blog updates Twitter through the official Google twitter integration app via feedburner. The twitter account doesn't use, and has never allowed, any other connections on Twitter.

Every week or so I see a new account in my follow list, always with locked tweets so nobody else can see them but me. Changing passwords solves nothing.

a) is someone accessing my account through google/feedburner and adding "followed" accounts?

b) is someone at twitter adding friends for me?

c) has a hacker found a way into my account?

d) does the new account even exist or is it some function/virus in my browser that makes me see accounts that really aren't 'followed'? (ie: something like the ad swaping adware that made the rounds recently)

e) other?

I can't stop accounts from appearing on my 'followed' list, I've been trying for 2 months. Help?