Denial of Service (DoS) attacks
A denial-of-service (DoS) is any type of attack where the attackers (hackers) attempt to prevent legitimate users from accessing the service. In a DoS attack, the attacker usually sends excessive messages asking the network or server to authenticate requests that have invalid return addresses. or "DoS" attacks are designed to make a service inaccessible.
DoS attacks that have been launched against high profile websites are frequently reported by the media. However, attacks on any type of system, including industrial control systems which support critical processes, can result in a denial of service.
When a website suffers a DoS attack, the apparent effect will depend on your perspective. For the average user, it appears that the site has simply stopped displaying content. For businesses, it could mean that the online systems they depend upon have ceased to respond. The An indication or sign of disease and illness. of a DoS attack against industrial control systems may include the inability to retrieve sensor data, or control critical processes.
DoS attacks can range in duration and may target more than one site or system at a time. An attack becomes a 'distributed denial of service', referred to as “DDoS”, when it comes from multiple computers (or vectors) instead of just one.
Symptoms of DOS attacks
- slows performance of the servers under attack and can completely halt any other access
- inability to access resources held on the server
Effects of DOS attacks
- Genuine users are not able to access resources, so may not be able to find the information or carry out the actions they need.
- Businesses may not be able to carry out time critical actions.
- They may suffer reputational damage.
- Customers may choose to use a competitor.
Costs of DOS attacks
- If unable to complete business in time, contracts may not be paid, resulting in financial loss.
- Employees may be required to work overtime to fix the faults, resulting in additional costs for pay.
Type of fault caused by DOS attacks
| Fault | Impact |
| Bandwidth Consumption | Flood of requests fills the connection up to their limit so no other requests can get through. The effect only lasts as long as the attack is maintained. |
| Resource Starvation | Requests each use a little bit of other resources, like disk space, until the server runs out and is no longer able to function correctly. |
| Domain Name Service (DNS) Attacks | These attack the servers that route internet traffic so can impact on multiple websites. |
| Fault | Bandwidth Consumption |
|---|---|
| Impact | Flood of requests fills the connection up to their limit so no other requests can get through. The effect only lasts as long as the attack is maintained. |
| Fault | Resource Starvation |
|---|---|
| Impact | Requests each use a little bit of other resources, like disk space, until the server runs out and is no longer able to function correctly. |
| Fault | Domain Name Service (DNS) Attacks |
|---|---|
| Impact | These attack the servers that route internet traffic so can impact on multiple websites. |
Reasons for DOS attacks
- Financial - The attacker may demand payment to stop the attack
- Political - The attacker may wish to take down government websites to protest at government actions
- Personal - An individual may have a grievance against a company and decide to enact revenge
