Are you certain no-one is recording all your keystrokes?
I try to make a habit of not storing passwords. Usernames yes, address details yes, but passwords no. Even if I were using auto form-fillers, and there was a high level of encryption, I would still not rest easy.
I realize, in order to break such forms software, a hacker would need ready access to my machine and he would need to have a copy of the forms software. These are not insurmountable hurdles to people with the skills and the time.
The troubles started quite mildly. For a while, every now and again (on average once a day at least), my pc cursor would freeze up. My pc would just decide to restart itself, so I would lose some of my work.
Anyway, I had security problems. What they were and what happened afterward you may follow on Online Protection Failure