|Anti-spam technique: Attention bonds|
|Date of first use:||2002|
|Difficulty of implementation:||High|
In an attention bond system, the sender of a message puts a sum of money in escrow as a bond warranting that the message is not spam. If the recipient decides that the message is, in fact, spam, the bonded money is transferred from escrow holder to recipient.
Attention bonds would impose an actual cost on spammers, both on 'pure' spammers and on otherwise legitimate organizations that occasionally spam.
Users who do not wish to participate in the system do not have to, in that they can opt to continue to receive e-mail with no bond required.
- Requires a working digital cash micropayment system with universal deployment and low transaction overheads. No such system exists, and financial organizations are motivated to avoid deploying one.
- Requires one or more trustworthy escrow organizations, as otherwise spammers will simply send e-mail with forged attention bonds.
- Requires that users be able to exempt certain senders from bond requirements, so that e-mail newsletters can still exist.
- If the system is poorly implemented with inadequate security, hijacked user accounts may result in financial cost to the victims.
- Requires a new protocol so that the sender's e-mail software can determine the bond required, and the user can be prompted as to whether to accept it.
- If users are allowed to set their own bond values, some people may set theirs so high that they are effectively cut off.
- Because of extreme variations in wealth between nations, people in poorer nations might find themselves cut off from e-mailing anyone in wealthy nations.
- Opinion polls suggest an extremely high level of resistance to any kind of financial cost potentially being involved in sending e-mail.
So far no system of attention bonds has been widely deployed, so the effectiveness it would have is widely debated.