Richard Clayton and I recently presented evidence of the adverse impact of take-down companies not sharing phishing feeds. Many phishing websites are missed by the take-down company which has the contract for removal; unsurprisingly, these websites are not removed very fast. Consequently, more consumers’ identities are stolen.

In the paper, we propose a simple solution: take-down companies should share their raw, unverified feeds of phishing URLs with their competitors. Each company can examine the raw feed, pick out the websites impersonating their clients, and focus on removing these sites.

Since we presented our findings to the Anti-Phishing Working Group eCrime Researchers Summit, we have received considerable feedback from take-down companies. Take-down companies attending the APWG meeting understood that sharing would help speed up response times, but expressed reservations at sharing their feeds unless they were duly compensated. Eric Olsen of Cyveillance (another company offering take-down services) has written a comprehensive rebuttal of our recommendations. He argues that competition between take-down companies drives investment in efforts to detect more websites. Mandated sharing of phishing URL feeds, in his view, would undermine these detection efforts and cause take-down companies such as Cyveillance to exit the business.

I do have some sympathy for the objections raised by the take-down companies. As we state in the paper, free-riding (where one company relies on another to invest in detection so they don’t have to) is a concern for any sharing regime. Academic research studying other areas of information security (e.g., here and here), however, has shown that free-riding is unlikely to be so rampant as to drive all the best take-down companies out of offering service, as Mr. Olsen suggests.

While we can quibble over the extent of the threat from free free-riding, it should not detract from the conclusions we draw over the need for greater sharing. In our view, it would be unwise and irresponsible to accept the current status quo of keeping phishing URL feeds completely private. After all, competition without sharing has approximately doubled the lifetimes of phishing websites! The solution, then, is to devise a sharing mechanism that gives take-down companies the incentive to keep detecting more phishing URLs.

Here is our stab at devising a suitable sharing mechanism. We propose the creation of a members-only sharing club with compensation for net contributors paid for by net receivers. Take-down companies submit real-time copies of their entire feeds to a trusted third party (for the sake of argument, let’s assume that the APWG takes on this role). The APWG collates the individual feeds, marks the source of each submission (i.e., which take-down company) along with a timestamp. The APWG makes the amalgamated feed available immediately to all members. The members pick out phishing URLs impersonating their own clients, while ignoring the rest. Crucially, the expensive task of verifying phishing URLs and initiating take-down continues to be performed by the take-down company.

Periodically, the combined feed is audited to determine the reciprocity of contributions. Take-down companies provide a list of their clients to the auditor. The auditor then computes the number of phishing websites impersonating each take-down company’s clients that are missed by the takedown company but identified by others. The auditor also tallies the time difference for phishing websites that are identified by others first.

For example, suppose bank A1 has hired take-down company A to remove phishing sites on its behalf, and bank B1 has hired take-down company B. Suppose 500 phishing sites impersonate A1, and that A identifies 400 while B identifies an additional 100 sites missed by A. Likewise, suppose another 500 phishing sites impersonate bank B1, and that B identifies 300 while A identifies an additional 200 sites missed by B. B has received a net of 100 useful phishing sites more from A than B has given to A. Consequently, B should pay A a previously-agreed ‘finder’s fee’ for identifying these extra 100 websites.

The ‘finder’s fee’ provides additional incentive for take-down companies to invest in better phishing website detection. Designed properly, such a sharing club can overcome the potential for free-riding that companies such as Cyveillance fret about, while increasing sharing to shorten phishing website lifetimes.

Some subtleties must be mentioned, however. If the finder’s fee is big enough, some companies may be tempted to cheat to minimize their payout. For instance, underperforming take-down companies could claim to have independently discovered missing data from their feed shortly after collecting it from the shared feed. This can be mitigated by adding a credible threat of detection — inserting a few dubious fake phishing URLs that only appear in the shared feed. If the company claims to have ‘independently’ rediscovered these URLs, then they will be caught cheating. Another issue is that the auditing system does incur some overhead, which could be avoided if sharing was made unconditional.

To sum up, we recognize that many take-down companies will be reticent to share. However, we feel that sharing is too important to the goal of tackling phishing to brush aside because of a few inevitable complications. For the good of protecting consumers, the anti-phishing industry should learn to co-operate!