F5 Networks survey of 1,000 medium and large organisations in 10 countries found that up to 45 percent of respondents experience such attacks on a regular basis. Nearly half had detected attempts to access encrypted data on networks, with 44 percent noticing attacks against DNS servers, one of the most difficult-to-defend assets. About half rated denial of service attacks as highly effective with 79 percent saying they still relied on firewalls to deflect them despite 42 percent finding that such devices were ineffective against conventional attacks at the network layer.”]