1. The Effects of Anti-Spam Methods on Spam Mail Eilon Solan, Tel Aviv University Eran Reshef, Blue Security Inc.

2. Fighting Spam Mail Three approaches of fighting spam mail: 1)Increasing cost of sending spam mail (authentication, counter attacks, payments (monetary or computational power), regulatory actions …) 2)Filters. 3)Do-not-spam registry Suppose the three approaches are technologically available. Which approach is better? Which approach lowers the amount of spam that spammers send, thereby improving the efficiency of the internet? Which approach lowers the amount of spam that users receive? Approach …

3. Fighting Spam Mail Three approaches of fighting spam mail: We provide a game-theoretic model that allows us to answer these questions. Which approach lowers the amount of spam that spammers send, thereby improving the efficiency of the internet? Which approach lowers the amount of spam that users receive? 1)Increasing cost of sending spam mail (authentication, counter attacks, payments (monetary or computational power), regulatory actions …) 2)Filters. 3)Do-not-spam registry Model …

4. The Model Users Spammers Model 2…

5. The Model Users Spammers Filters “Rich” Users “Poor” Users Model 3…

6. The Model Potential Buyers Users Spammers Filters Method “Rich” Users “Poor” Users

7. We take the users as dummies: 1) They cannot upgrade their filter. 2) They do not disconnect from the internet. Method The decision of each spammer: How much spam messages to send to each user. We study the stable behavior of the system: No spammer can improve profitability by slightly changing the amount of spam messages he/she sends. We study how the three technologies mentioned above affect the stable behavior. Results …

8. Increasing cost of sending spam: Results Has an unambiguous positive effect: Reduces the amount of spam spammers send. Reduces the amount of spam users receive. Results - Filters…

9. Increasing cost of sending spam: Results Improving filters: Has an unambiguous positive effect: Reduces the amount of spam spammers send. Reduces the amount of spam users receive. Has an ambiguous effect: Users who have the improved filter receive less spam. If the cost of sending spam is not high, the total number of spam spammers send increases. Results - Registry…

10. Results Do-not-spam Registry: Has an ambiguous effect: Users who register stop receiving spam. If the cost of sending spam is not high: having poor users register increases the amount of spam sent by spammers. having rich users register lowers the amount of spam sent by spammers. Conclusions… If the cost of sending spam is high: having poor users register lowers the amount of spam sent by spammers. having rich users register increases the amount of spam sent by spammers.

11. Increasing the cost of sending spam: Conclusions Offer filters and a registry free of charge to home users: Without such a measure, improving filters only makes the internet more crowded, and causes users who do not use the improved filter to receive more spam. Improving filters, or having a do-not-spam registry, may harm users who cannot afford them. Therefore the socially responsible solution is to offer filters and the use of a registry for free to those users. The End!