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Windows users and Internet routing equipment are the latest pawns of malicious intruders intent on launching denial of service attacks online, an expert from Carnegie Mellon's CERT Coordination Center warned network operators here Monday.

So-called distributed denial of service (DDoS) attacks rely on an attacker's ability to install malicious agents on a large number of computers, and use them to simultaneously flood a victim with overwhelming traffic. The shift from Unix machines to Windows computers began in late 2000, said Houle, and has grown noticeably in recent months.

The mechanisms for controlling large numbers of compromised boxes have also changed, said Houle, becoming vastly more sophisticated since DDoS attacks began in 1999. Attackers increasingly use IRC -- the Internet's chat room systems -- to direct attacks, sometimes using domain name records as a kind of dead drop for directing their agents to a particular IRC server.

More disturbing to network operators, attackers have taking over the machines that route and direct the flow of Internet traffic, to use them as weapons, Houle said.

"What we see are routers with default and weak passwords being targeted," Houle said. After cracking a router, attackers can use it to launch straightforward denial of service attacks against an Internet site. Because routers can generate enough traffic to impede an end host, while standing up well to a similar counterattack, it's become a valued platform for cyber vandals engaged in online skirmishes in the mostly-juvenile computer underground.

"If I'm an intruder and I want to be well protected against people DoSing me, a router is somewhat better than an end host," said Houle.

The development is foreboding, Houle said, because of the possibility that attackers could begin targeting the protocols that link routers to one another, potentially leading to disruptions in the Internet's fundamental infrastructure. "This is stuff that's being talked about, not just within the security community, but also the intruder community," said Houle.

Generally, speakers at NANOG agreed that conditions haven't improved much since February 2000, when a fifteen-year-old Canadian boy used distributed denial of service tools to flood sites like eBay, CNN.com and Yahoo! with traffic, knocking them offline.

In fact, attackers are now able to marshal so many machines in a DDoS attack, that they seldom bother to tamper with the packets to disguise their source. "If you have 200 compromised machines, it doesn't matter if the source addresses are spoofed or not," said Jason Slagle, network administrator at Toledo Internet Access, an Ohio ISP.

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