Business Communications Review has an article entitled The Botnet Threat reviewing a recent report put out by Arbor Networks, which surveyed ISPs about their biggest security concerns.
"When they surveyed 55 ISPs, McPherson and Labovitz discovered that distributed denial of service attacks, and the related threat of botnets, remain the biggest security problem that ISPs face. Together, these two elements were named as the top threat by 77 percent of respondents. "Brute-force attacks remain the most predominant attack type on the Internet today," the authors write.
The largest sustained attack reported by the survey respondents was a whopping 17 Gbps; a UDP flood of 22 million packets per second (pps) and a SYN flood of 14 million pps have also been reported. "The magnitude of these attacks is incredible when you consider that a 14 Mpps SYN flood can nearly fill an entire OC-192 (10 Gbps) circuit with a minimum packet size," McPherson and Labovitz write. "Any one of these attacks, or even a fraction thereof, can create significant pain for even the largest ISP networks in the world today."
The report also cites what the authors call "a new and disturbing observation" made by one respondent: Not only are botnets highly organized and "uniformly gargantuan," but there's an increasing amount of marketing of these botnets. ("Blast your affiliate numbers overnight!" is a typical pitch they report seeing.)"