Deleting saved passwords and login information is a prudent measure to enhance the security of any online activity involving the sites that login information is used for. However, it is not a critical security step, and generally can be disabled without a significant increase of risk.
To prevent Privacy Controls from removing this information in future:
- Open Privacy Controls and go to Options along the left hand side.
- Select the More Info button along the right hand side, next to the internet browsing history section.
- Expand the category that corresponds to the browser you use by clicking the + (plus sign) besides that browser.
- Now deselect saved passwords, along with any other categories you do not wish to have cleaned.
- Please make sure any categories you do not wish to have removed are unchecked. Depending on the level of security and the types of information stored on sites you commonly access you may also want to deselect Cookies, Favorites, History (visited sites), and Auto-Complete form data.