Peak-time distributed denial-of-service attacks cost organizations more than $100,000 per hour, said half of the respondents to a new survey of mid-sized and large corporations in the U.S. and Europe.
And for a third of respondents, the average peak hourly revenue loss was more than $250,000.
However, shutting down attacks took time. Only 26 percent said it took them less than an hour, while 33 percent said it took between one and two hours, and 40 percent said it took more than three hours.
By comparison, a year ago, only 32 percent of companies said that they would lose more than $100,000 an hour, and 68 percent said it took them less than two hours to respond to an attack.
"The cost is going up," said Rodney Joffe, senior vice president and fellow at Neustar, which sponsored the research. Harris Interactive helped conduct the survey.
Financial services were particularly hard hit, he added, with 20 percent of financial service organizations losing more than $1 million in hourly revenues. And 43 percent reported their losses at more than $250,000 per hour.
Financial firms are particularly adept at calculating these costs, he added. "They can tell you the loss of revenues down to the second," he said.
According to the survey, 62 percent of financial organizations were attacked more than once -- a third were attacked more than five times. As a result, 79 percent said that they're investing more money in fending off DDoS attacks this year compared to last.
[ RELATED: DDoS attacks are more than disruptions to service ]
Overall, 76 percent of companies are investing more in DDoS protection than in 2014 and 47 percent of the attacked organizations are participating in security consortiums to share information on threats and counter measures.
And it's not just about loss of revenues. Companies also reported that DDoS attacks were used to cover up financial thefts, theft of intellectual property and customer data, and damage to networks or equipment.
And 45 percent of respondents said that the DDoS attacks were also used to install or activate malware, often ransomware, which, in turn, could cost companies even more money to deal with.
The size of the DDoS attacks was also up this year, with 53 percent of respondents saying they were 5Gbps or higher, enough to cause a serious service disruption, a significant increase over last year.
The motivation for the DDoS attacks is now mostly financial, Joffe added.
"The general hijinks, the social attacks, are diminishing," he said.
In fact, it is becoming increasingly difficult to differentiate criminals attacks from those sponsored by nation states.
"Now it's become intertwined," he said. "The criminals have generated so much revenue that they support and fund local political processes."