Ataque contra Nodo50
Nodo50: Demanding our right to communicate freely
18th of January of 2002
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On Thursday 17th of January, 2002, Nodo50 suffered a denial of service attack aimed at our Web Server. This anonymous action meant that the WebSites of over 400 organisations hosted by Nodo50 ( were inaccessible for 18 hours, to site owners and to the thousands of people who visit the sites daily.

The Assembly of Nodo50 considers the mass media's recent coverage of the work of the "Network of Counterinformation EU 2002" (1) to be an attempt by law enforcement and mainstream media to criminalize legitimate work, misinform the public and engineer an atmosphere encouraging the type of attack Nodo50 has experienced. The original report was published by the Colpisa agency and can be found here:

It is not the first time that law enforcement and journalists have come together to generate such an environment. Nor is it the first time that Nodo50 has been the target of such attacks. It is common here for this mix of ghosts and misinformation to aim to turn public opinion against perfectly legitimate and legal actions through insinuations of criminal activitiy. People have the right to inform and to inquire freely and thus protect against attempts to seed a cycle of suspicion that encourages justification for attacks such as we have experienced.

Considering that Spain has recently taken up presidency of the European Union, we are aware that this will not be the last attack. The Spanish Government will attempt to continue with actions that repress legitimate actions of people and organisations opposed to their policies and positions, in the interest of protecting and representing interests of Bankers and multinationals in Europe.

To identify our political work with those they label "the violent ones" is a self-interested simplification of the work of thousands of organizations who communicate through the Nodo50 network.

We will continue fighting for our right to communicate and express ourselves freely. Though our means may be modest, we will continue with absolute firmness and conviction.

Assembly of Nodo50

(1) The"Network of Counterinformation EU 2002" is a network of Internet Service providers and websites who aim to facilitate alternative information during the spanish presidence of the European Union


  Someone or some group launched a denial of service attack (DoS) against the Web server of Nodo50. The technical description of this attack is below.

For 24 hours, these attackers used the DoS technique called SYN flooding. SYN flooding exhausts the webserver with requests that the server cannot understand. SYN flooding takes advantage of one the vulnerabilities of the design of the TCP. In a normal TCP conversation, the client sends a SYN packet, and the server replies with a packet SYN/ACK, and the client sends a third packet confirming the client got the server's packet ACK. These three messages establish a valid and working TCP connection.

In a SYN attack, the attacker modifies this normal interaction by never sending the third and completing packet. The attacker sends numerous SYN packets with a forged (false) return address. The server acknowledges these initial SYN packets and waits for a final confirmation packet. But the attacker never sends the final confirmation packet. The server uses resources in waiting for the final packet, so if it waits for too many false connections, it does not have enough resources to attend to real requests.

esquema DoS

For a more detailed description of this TCP vulnerability, please have a look to:

paquetes SYN

Nodo50 looked at the forged SYN packets, including the IP address of the origin packets. We determined that the attackers were using the SYN flooder called 'juno-z'.

At 18:00 PM on Thrusday Jan 17, Nodo50 we were able to defend against the attack. We could defend against it by dynamically filtering all packets that had the signature of the 'juno-z' flooding stopped the attack.

The attackers stopped the SYN flooding at 12:13 AM 18/01/02.