The Effects of Anti-Spam Methods on Spam Mail

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The Effects of Anti-Spam Methods on Spam Mail
Eran Reshef, Blue Security Inc.
Eilon Solan, Tel Aviv University
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Fighting Spam Mail
Three approaches of fighting spam mail

• Increasing cost of sending spam mail
• (authentication, counter attacks, payments
  (monetary or computational power), regulatory
  actions )
• Filters.
• 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
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Fighting Spam Mail
Three approaches of fighting spam mail

• Increasing cost of sending spam mail
• (authentication, counter attacks, payments
  (monetary or computational power), regulatory
  actions )
• Filters.
• Do-not-spam registry

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?
We provide a game-theoretic model that allows us
to answer these questions.
Model
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The Model
Model 2
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The Model
Filters
Rich Users
Poor Users
Model 3
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The Model
Filters
Rich Users
Poor Users
Method
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Method
We take the users as dummies 1) They cannot
upgrade their filter. 2) They do not disconnect
from the internet.
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
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Results
Increasing cost of sending spam
Has an unambiguous positive effect Reduces the
amount of spam spammers send. Reduces the amount
of spam users receive.
Results - Filters
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Results
Increasing cost of sending spam
Has an unambiguous positive effect Reduces the
amount of spam spammers send. Reduces the amount
of spam users receive.
Improving filters
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
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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.

• 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.

Conclusions
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Conclusions
Increasing the cost of sending spam
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.
Offer filters and a registry free of charge to
home users
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!