Many companies remain vulnerable to attacks against domain name system servers, despite efforts to secure them, according to a new study.

More than half the respondents to a Mazerov Research and Consulting study reported having fallen victim to some form of malware attack. More than one-third had been hit by a denial-of-service (DoS) attack, and more than 44 percent had experienced a pharming or cache-poisoning attack.

External and internal DNS servers were equally vulnerable: Both types succumbed to attacks with roughly the same frequency, interviews with 465 IT professionals found.

A DNS server compromised by a hacker could be used to funnel web surfers to all sorts of malicious websites, and could cause havoc with directory services and email, said Paul Mockapetris, the father of the DNS technology, earlier this year.

"Once you control the DNS server, you have licence to do phishing and pharming attacks and mislead all the users of that DNS server," said Mockapetris, who in 1983 proposed the DNS architecture and is acknowledged, along with the late Jon Postel, as the technology's inventor.

According to the Mazerov study, DoS attacks are prevalent among the respondents. Only 16 percent had never experienced one, but more than 10 percent said they often or frequently are hit by DoS attacks. A surprisingly high 41 percent of respondents experience DoS attacks.

The study found that the top forms of DNS attack are malware (worms, viruses, Trojans and so forth), 68 percent; denial of service, 48 percent; cache poisoning, 36 percent; and pharming, 23 percent.

Patching seems to be the method of choice for protecting DNS. Three quarters of all respondents devote valuable resources to patching their operating systems continuously. Others reported having to harden operating systems; invest in dedicated firewalls; and add DNS appliances, DoS mitigation services and other network security devices. On average, respondents used at least 3.5 overlapping methods to shore up their DNS security.

The study also looked at how long respondents' companies could weather DNS being taken offline before significant problems occurred, IT personnel were more sensitive to the issue than those occupying C-suites.

According to the study, C-level executives estimated they could withstand losing Internet connectivity for slightly more than two hours (126 minutes), whereas IT managers estimated significant problems would arise after 105 minutes. Other IT personnel - who may be most directly responsible for maintaining Internet uptime - estimated an even shorter time frame - an average of 72 minutes.

Respondents also were asked to assess what the probable impact would be on the health of their company if they were to experience a loss of Internet connectivity for a significant period of time. Maybe most alarming was that 12 percent of participants claimed they would be extremely or somewhat likely to go out of business completely, the study said.