spamming transactions attack

[b00f]

Description

We recently faced a spamming attack where numerous transactions were broadcasted across the network.
For instance, take a look at block 739070.
The spammer sent many transactions with small or zero amount, hoping to disrupt the blockchain.
This attack significantly impacted block creation and increased block time, as most of the network resources were engaged in validating these spam transactions.

How to Reproduce

This issue can be replicated by scripting transactions with zero or minimal amounts sent to random addresses in Testnet.

What Happened

As a result, some nodes crashed, causing the blockchain to halt for several hours.

Expected Behavior

One straightforward solution to prevent such malicious behavior is to impose a minimum transaction value for inclusion in the transaction pool. This parameter is configurable and does not affect consensus parameters. Each node can set its own threshold; for instance, a default of 0.1 PAC seems reasonable. This measure ensures that attackers must spend money to execute spam transactions, mitigating similar disruptive actions in the future.