From a basic computer security point of view, which of the following is the most common way for a virus to enter and infect a computer hard disk on a typical home or office system?

Introduction / Context:
This question examines basic awareness of how computer viruses spread, which is an important topic in computer security and general computer knowledge. Understanding common infection routes helps users avoid risky behaviour and protect their data. While viruses can spread in many ways, some methods are far more common in everyday environments.

Given Data / Assumptions:

• The focus is on the most common way a virus gets into a computer hard disk.
• The context is a typical user environment, such as home or office computers connected to the internet.
• Options include installing games from CD ROMs, opening emails, uploading pictures, sending emails and printing documents.
• We assume users may receive unsolicited or suspicious emails containing attachments or links.

Concept / Approach:
Viruses and other malware often spread through email messages that contain infected attachments or malicious links. When users open these attachments or click the links, the malware is executed and can infect the system. Although removable media and pirated software are also common sources, exam questions about modern threats frequently highlight email as the most common infection vector. Simply sending emails from your own account is not risky, but opening infected emails certainly is. Uploading pictures or printing documents are usually safe, unless special exploits are involved, which is less common in basic exam contexts.

Step-by-Step Solution:
Step 1: Consider how users interact with unknown content most frequently. They receive many emails every day. Step 2: Cyber criminals often send viruses attached to emails or hidden in links that appear to be from trusted contacts or organisations. Step 3: When an unsuspecting user opens an infected attachment or clicks a malicious link, the virus can execute and copy itself to the computer hard disk. Step 4: Installing games from original CD ROMs purchased legally is usually safe because the discs are checked by the publisher. The exam treats this as a low risk option. Step 5: Uploading personal photos from a mobile phone to a computer is generally a one way transfer of content and not a primary virus infection route in basic exam scenarios. Step 6: Sending emails from your own account does not introduce new files to your system and therefore does not normally cause an infection. Step 7: Printing documents uses data already on the system and is not in itself a typical method of virus entry. Step 8: Therefore, among the given choices, the most common way a virus infects a hard disk is by opening email attachments or links in suspicious emails.

Verification / Alternative check:
Security awareness guides frequently warn users not to open attachments or click links in unsolicited or unexpected emails. Many malware outbreaks in history, including famous email worms, have spread primarily through email systems. Antivirus companies list email borne malware as a major threat and advise scanning attachments before opening them. This emphasis in security literature supports the exam style answer that opening suspicious emails is a very common infection method.

Why Other Options Are Wrong:
Installing games from original CDs is mostly safe, although pirated or untrusted discs could be risky, which is not the scenario described. Uploading pictures from a phone generally transfers only image data and is a minor risk compared to email threats. Sending emails does not introduce new files to the local system. Printing documents is a simple output action and is not a standard infection vector in basic computer awareness questions.

Common Pitfalls:
A common mistake is to think that any file transfer from external media is equally dangerous. While removable media can indeed carry viruses, exam questions often highlight email because it combines ease of mass distribution with user trust. Always pay attention to the phrase most common and to the context of internet connected systems when choosing answers.

Final Answer:
The most common way for a virus to infect a computer hard disk is by opening email attachments or links in suspicious emails.