After moving to the United States, I have come across this reassuring statement fairly often:
<Product name> only has read access to your accounts. Nobody can authorize any transactions on your behalf, not even <product name>.
This is a particularly popular thing for services like Mint and Credit Karma to say in an effort to get you to give up the holiest of holies: The login credentials to your online banking accounts. This “guarantee” is also completely false, or at least incredibly deceptive.
There’s no such thing as “read-only access” to your Chase banking or American Express card accounts. Services like Mint and Credit Karma store your real usernames and passwords on their servers, not some kind of read-only token. If their servers get compromised, your linked bank accounts may very well be fully compromised as well.
Here’s the kicker: These services know this full-well. When you sign up for any of them, you’re agreeing that they bear no responsibility in the case of a compromise. (Read the fine print.) Your money is now gone, and they won’t be there to help you. FDIC won’t help you either—that only protects you if your financial institution becomes insolvent, not if your accounts are compromised.
What these companies actually seem to mean when they say that their access is “read-only” is that there is no functionality within their interfaces which allows people to authorize transactions and perform other changes, not that the credentials they’re storing can’t be used to do absolutely anything on your accounts. (The former borders on the irrelevant, of course, and the latter is what most people actually care about.)
Carefully evaluate whether you want to trust these companies based on these “protections” and the way they present them, and remember they won’t be there for you if things go wrong.
(To give a little perspective: Intuit, the company that develops Mint, Quicken, and QuickBooks, lets you encrypt your Quicken data file using a password, but only allows that password to consist of 15 characters or less. This is their supposedly “military-grade security system;” 15 characters isn’t even enough to reach 128-bit security, the lowest acceptable level for strong security.)
If you’re currently using any of these services, and want to reduce your risk, deleting your linked accounts within the service and/or the service account itself, as well as changing the password for each of your linked accounts should do the trick.