Threats for clients:

1. Viruses:
- Viruses are malicious software programs that can infect a client's computer.
- They can replicate themselves and spread from one computer to another.
- Viruses can cause damage to files, slow down the system, or even render it completely unusable.
2. Worms:
- Worms are also malicious software programs that can replicate and spread across networks.
- Unlike viruses, worms do not require a host file to attach themselves to.
- They can exploit vulnerabilities in a client's computer or network, causing damage and spreading themselves.
3. Trojan Horses:
- Trojan horses are disguised as legitimate software programs but contain hidden malicious code.
- They may be downloaded and executed by clients unknowingly.
- Once activated, trojan horses can steal sensitive information, damage files, or allow unauthorized access to the client's computer or network.
4. All of these:
- All the threats mentioned above (viruses, worms, and trojan horses) pose a significant risk to clients.
- Each of these threats can lead to data loss, privacy breaches, financial loss, or system malfunction.
In conclusion, clients should be aware of these threats and take necessary precautions, such as using antivirus software, keeping their systems and software up to date, and practicing safe browsing habits, to protect themselves from these potential risks.

Threats for Clients

There are several types of threats that can pose risks to clients' systems and data. In this case, the correct answer is option 'D', which states that all of the following are threats for clients: viruses, worms, and Trojan horses. Let's take a closer look at each of these threats.

1. Viruses:
- Viruses are malicious software programs that can infect a client's computer system by attaching themselves to files or programs.
- They can spread from one computer to another, often through email attachments, infected websites, or shared files.
- Once a virus infects a client's system, it can cause a range of issues, such as data corruption, system crashes, and unauthorized access to personal information.

2. Worms:
- Worms are similar to viruses, but they don't require user interaction to spread.
- They can replicate themselves and spread across networks, exploiting vulnerabilities in operating systems or software.
- Worms can consume network bandwidth, slow down computer performance, and even delete or modify files.
- They can also be used to create botnets, which are networks of infected computers controlled by a malicious attacker.

3. Trojan Horses:
- Trojan horses are deceptive software programs that appear legitimate but contain hidden malicious code.
- They are often disguised as useful applications or files, enticing users to download and install them.
- Once a Trojan horse is executed, it can perform various actions, such as stealing sensitive information, modifying or deleting files, and providing unauthorized access to the attacker.
- Unlike viruses and worms, Trojan horses do not self-replicate.

Conclusion:
All of these threats (viruses, worms, and Trojan horses) can pose significant risks to clients. They can compromise the security, integrity, and confidentiality of data, disrupt system operations, and lead to financial losses or identity theft. It is crucial for clients to have robust security measures in place, such as antivirus software, firewalls, and regular system updates, to mitigate these threats and protect their systems and data.