Some 20% of respondents have no DDoS protection in place.
About 22% of UK organisations had experienced a disruptive distributed denial-of-service (DDoS) attack in 2012, according to a new report.
Neustar report also revealed that 37% of attacks lasted over 24 hours, while 22% lasted over a week compared to 13% in North America.
The UK survey report also said that the telecommunications (53%), ecommerce (50%) and online retail (43%) were hit with higher rates of attack, compared to the financial sector (44%) in North America.
According to analysts, recent attacks on US banks have enabled others to copy the tactics, including the recent DDoS attacks against Dutch banking systems in April 2013.
During the attacks, financial services and telecommunications firms experienced the highest downtime leading to heavy losses from an outage, with 26% of all attacks on the financial sector having a revenue impact of over £100,000.
Neustar Enterprise Services VP Alex Berry said that DDoS attacks will continue to be part of the modern threat landscape because they are easy and relatively low-cost to perpetrate.
"They continue to be a threat to both large and small firms in all industries," Berry said.
"Some of the recent large attacks have opened doors for even more malicious attackers to adopt similar tactics and Neustar fully expects to see the impacts of these attacks grow in line with their increasing complexity.
"As in North America, our survey has found that UK companies are hoping traditional defences will suffice, but given the frequency of attacks and the impact when sites go dark, such hopes are often badly misplaced."