Web security company CloudFlare on Monday evening battled a massive distributed denial of service (DDoS) attack that has eclipsed Spamhaus as the largest-ever such assault.

The attack, targeting one of CloudFlare's clients, peaked yesterday "just shy" of 400 gigabits per second, the company's CEO Matthew Prince told PCMag. In comparison, last year's record-breaking attack on Spamhaus reached 300 Gbps. A "normal" DDoS attack that might take down a bank website, for instance, is around 50 Gbps.

"The attack wasn't extraordinary except that it was quite large," Prince said.

Very big NTP reflection attack hitting us right now. Appears to be bigger than the #Spamhaus attack from last year. Mitigating.

— Matthew Prince (@eastdakota) February 10, 2014

Attackers leveraged weaknesses in the Network Time Protocol (NTP), which is used to synchronize computer clocks, to flood the European servers with data. While researchers have long-predicted that NTP might someday become a vector for DDoS attacks, the trend has only recently become popular, causing an issue for some gaming websites and service providers, CloudFlare wrote in a blog post last month.

"This vector has been rising in popularity over the last 6 months and is now responsible for some of the largest attacks we mitigate across our network," Prince said. "NTP amplification takes advantage of misconfigured network time servers (the systems used to synchronize clocks across servers)."

Monday's attack targeted a single customer, but it was so large that it affected CloudFlare's entire global network. The company did not reveal which of its customers was targeted.

"We were able to mitigate the attack but did see network congestion (slowness) in Europe at the peak of the attack," Price said.

DDoS attacks aim to overload a victim's servers by flooding them with more data than they can handle. Such attacks can disrupt a victim's business, or knock its website offline.

Experts now warn that this attack could be just the tip of the iceberg. Until all the misconfigured NTP servers are cleaned up, attacks of this nature will continue. Network administrators can see whether they are running a misconfigured NTP server by visiting the Open NTP Project.

"Someone's got a big, new cannon. Start of ugly things to come," Prince tweeted Monday. "These NTP reflection attacks are getting really nasty," he added.

For more, check out Understanding the SpamHaus DDoS Attack.