Archive for November, 2012

Iszi chose this week’s question of the week, Tom Marthenal‘s “Why do we lock our computers?” – as Tom puts it:

It’s common knowledge that if somebody has physical access to your machine they can do whatever they want with it, so what is the point?

This one attracted a lot of views, as it is a simple question of interest to everyone.

Both Bruce Ediger and Polynomial answered with the core reason – it removes the risk from the casual attacker while costing the user next to nothing! This is an essential factor in cost/usability tradeoffs for security. From Bruce:

The value of locking is somewhat larger than the price of locking it. Sort of like how in good neighborhoods, you don’t need to lock your front door. In most neighborhoods, you do lock your front door, but anyone with a hammer, a large rock or a brick could get in through the windows.

and from Polynomial:

An attacker with a short window of opportunity (e.g. whilst you’re out getting coffee) must be prevented at minimum cost to you as a user, in such a way that makes it non-trivial to bypass under tight time constraints.

Kaz pointed out another essential point, traceability:

If you don’t lock, it is easy for someone to poke around inside your session in such a way that you will not notice it when you return to your machine.

And zzzzBov added this in a comment:

…few bystanders would question someone walking up to a house and entering through the front door. The assumption is that the person entering it has a reason to. If a bystander watches someone break into a window, they’re much more likely to call the authorities. This is analogous with sitting down at a computer that’s unlocked, vs physically hacking into the system after crawling under a desk.

It removes a large percentage of possible attacks – those from your co-workers wanting to mess with your stuff – thanks enedene.

So – protect yourself from co-workers, casual snooping and pilfering and other mischief by simply locking your machine every time you leave your desk!

Liked this question of the week? Interested in reading it or adding an answer? See the question in full. Have questions of a security nature of your own? Security expert and want to help others? Come and join us at security.stackexchange.com.

” What is the impact of disclosing the front face of a credit card?” and “How does Amazon bill me without the CVC/CVV/CVV2?” are two questions which worry a lot of people, especially those who are aware of the security risks of disclosing information, but who don’t fully understand them.

Rory McCune‘s question was inspired by a number of occasions where someone was called out for disclosing the front of their credit card – and he wondered what the likely impact of disclosing this information could be, as the front of the card gives the card PAN (16-digit number), start date, expiry date and cardholder name. Also for debit cards, the cardholders account number and sort code (that may vary by region).

TC1 asked how Amazon and other individuals can bill you without the CVV (the special number on the back of the card)

atdre‘s answer on that second question states that for Amazon:

The only thing necessary to make a purchase is the card number, whether in number form or magnetic. You don’t even need the expiration date.

Ron Robinson also provides this answer:

Amazon pays a slightly higher rate to accept your payment without the CVV, but the CVV is not strictly required to present a transaction – everybody uses CVV because they get a lower rate if it is present (less risk, less cost).

So there is one rule for the Amazons out there and one rule for the rest of us. Which is good – this reduces the risk to us of card fraud. Certainly for online transactions.

So what about physical transactions – If I have a photo of the front of a credit card and use it to create a fake card, is that enough to commit fraud?

From Polynomial‘s answer:

On most EFTPOS systems, it’s possible to manually enter the card details. When a field is not present, the operator simply presses enter to skip, which is common with cards that don’t carry a start date. On these systems, it is trivial to charge a card without the CVV. When I worked in retail, we would frequently do this when the chip on a card wasn’t working and the CVV had rubbed off. In such cases, all that was needed was the card number and expiry date, with a signature on the receipt for verification.

So if a fraudster could fake a card it could be accepted in retail establishments, especially in countries that don’t yet use Chip and Pin.

Additionally, bushibytes pointed out the social engineering possibilities:

As a somewhat current example, see how Mat Honan got hacked last summer :http://www.wired.com/gadgetlab/2012/08/apple-amazon-mat-honan-hacking/all/ In his case, Apple only required the last digits for his credit card (which his attacker obtained from Amazon) in order to give up the account. It stands to reason that other vendors may be duped if an attacker were to provide a full credit card number including expiration dates.

In summary, there is a very real risk of not only financial fraud, but also social engineering, from the public disclosure of the front of your credit card. Online, the simplest fraud is through the big players like Amazon, who don’t need the CVV, and in the real world an attacker who can forge a card with just an image of the front of your card is likely to be able to use that card.

So take care of it – don’t divulge the number unless you have to!

Liked this question of the week? Interested in reading it or adding an answer? See the question in full. Have questions of a security nature of your own? Security expert and want to help others? Come and join us at security.stackexchange.com.