You may (or may not) have heard that some iTunes accounts have been hacked recently. One incident was a developer who managed to elevate all his products into the top 50 which made them look really popular. Other more isolated incidents have been to use the hacked accounts to purchase downloads, though no one is quite sure how the perpetrator managed to gain anything worthwhile.
Anyway, the recommendation is that you change you iTunes password, as always, but also to remove any automatic credit card from the account. This is a good recommendation in any case because these card details held by vendors just in case you should happen to pass by again are at risk if anything subverts their systems.
The snag is, if you don’t happen to have your iTunes registered system with you, either iP* device or computer, then how do you change your account. There is no obvious web site you can login to except by starting up the iTunes software which you don’t have. What is not widely known is that the “Apple-id” that you use to purchase from the Apple web store is actually the same account so you can reset it there. Go to www.apple.com, change to your correct country (at the bottom of the screen), move to the Store and then, at the top right is an “Account” button. Login there and change you details as required.