How Attackers Stay Hidden, Watch Activity, and Take Over Systems 👀🔐
In the previous article, Part 1, we explored how software-based attacks gain entry through vulnerabilities and spread using exploits, viruses, and worms. This article builds on that foundation by examining what attackers do after they gain access—how they hide, monitor activity, and take control of systems. 👉 Software Security Threats_1
This article focuses on threats that quietly embed themselves into systems to hide their presence, monitor user activity, and maintain ongoing control. Because these attacks often run in the background without obvious signs, they can remain active for long periods and cause significant damage before being discovered.
Adware 📢⚠️
Adware is software that displays unwanted advertisements on your computer. The most common form of adware appears as a browser add-on or toolbar that claims to provide helpful features such as advanced search options. However, once installed, it often causes frequent pop-up ads to appear whenever you browse the web.
Adware creators make money when users click on these ads. Strictly speaking, not all adware is illegal, nor are all adware developers involved in criminal activity. If you willingly install a toolbar or application and later decide it shows too many ads or isn’t worth the value it provides, you are usually free to remove it.
Real-world analogy:
Think of adware like a free newspaper stand placed inside your living room. At first, it seems harmless and even beneficial. But soon, flyers start falling everywhere, ads interrupt your conversations, and removing the stand turns out to be harder than expected.
Removing adware is not always easy. The uninstall option may or may not appear in Add or Remove Programs in Windows. In some cases, you may need to visit a specific website or follow extra steps to remove it entirely. Some adware is purely an annoyance, with no attempt to disguise itself as something valuable. These programs can be challenging to remove, much like a virus infection.
Anti-malware software may help in some cases, but you may also need to perform a web search for manual removal instructions, such as editing the system registry, to eliminate stubborn adware completely.
Spyware 🕵️♂️⌨️👀
Spyware is software that secretly monitors and records your computer usage. This includes programs like keyloggers, which record everything you type, as well as software that tracks the websites you visit, the links you click, and the ads you interact with. This collected information is then sent back to the spyware’s creators.
Spyware developers make money by collecting consumer marketing data, whether about individual users or large groups. Unlike adware, most spyware is illegal and operates without your knowledge or consent. It typically runs quietly in the background and can be challenging to detect and remove.
Real-world analogy:
Think of spyware like someone standing behind you, quietly taking notes every time you use your computer—recording what you type, where you go, and what catches your attention—without you ever realizing they are there.
Spyware does not replicate itself like a virus. Instead, it spreads through low-level social engineering, tricking users into installing it themselves. The most common way to get infected is by downloading free software from untrusted websites. This is why it’s important to be extremely cautious when downloading executable (.exe) files.
Some websites advertise software as a “great deal” simply because it’s free. Still, many unscrupulous site owners, especially in specific high-risk industries like adult entertainment, exploit visitors by infecting their systems with spyware or adware.
Many anti-malware programs can detect and remove spyware. There are also tools explicitly designed to remove spyware and adware, such as Microsoft Defender, which provides built-in protection for Windows systems.
Ransomware 💰🔐⚠️
Ransomware is a particularly insidious type of malware that extorts money from infected users. Although ransomware has existed since 1989, it did not become widespread until around 2012. It is usually delivered via a Trojan program or by exploiting software vulnerabilities.
Once active, ransomware displays a message demanding payment or facing consequences. Some versions try to appear official. For example, one variant posed as an official notice from a law enforcement agency, claiming the user had violated the law and must pay a fine to resolve the issue. Other versions are more direct.
Real-world analogy:
Ransomware is like someone breaking into your house, locking all your doors, and demanding money to give you the keys back—with no guarantee they’ll keep their promise.
Many ransomware attacks encrypt files on the hard drive and demand payment to restore access. This type of attack is known as cryptoviral extortion. The ransomware often provides a convenient payment link that redirects the victim to another website to enter payment details.
Clicking these links introduces additional risks. Visiting the payment site can lead to the installation of additional malware, such as rootkits, spyware, or keyloggers. Attackers may also request credit card information, creating further opportunities for fraud.
Fortunately, most anti-malware software can detect and block ransomware. If a system is already infected and files are locked or encrypted, the only reliable recovery option may be to wipe the system and restore from a clean backup, assuming the backup itself has not been infected.
Rootkits 🥷🖥️🔒
Rootkits are software programs designed to hide certain activities or components from the operating system. They do this by gaining administrator-level (root) access, which allows them to operate at a very deep level within the system.
With a rootkit installed, there may be processes running that do not appear in Task Manager, or network connections that do not show up in network monitoring tools. The rootkit deliberately masks the presence of these activities.
Real-world analogy:
A rootkit is like someone wearing an invisibility cloak inside your house—they move around, open doors, and use your resources. Still, your security cameras and motion sensors never detect them.
Rootkits achieve this by manipulating the operating system so that information that would typically be visible is filtered out or hidden. Unfortunately, many rootkits are specifically written to evade anti-malware programs, especially outdated ones.
Because rootkits are so difficult to detect once installed, the best defense is to carefully monitor system behavior and catch them during installation, before they become fully embedded in the operating system.
Backdoors 🚪🕳️⚠️
A backdoor is a method of bypassing a computer’s standard security mechanisms. Instead of needing a username and password, an attacker who knows about the backdoor may be able to log in without providing any credentials.
Backdoors can exist as standalone programs or be embedded in other types of malware, such as rootkits or worms. In these cases, the backdoor provides attackers with continued access to the system even after the initial compromise.
Real-world analogy:
A backdoor is like a hidden door in a locked building. Even though the front door is secured with locks and alarms, someone who knows about the secret entrance can walk right in without triggering regular security checks.
Not all backdoor problems are caused by hackers. User error is another common source. For example, failing to change a default password can unintentionally leave a system wide open to unauthorized access. Additionally, debugging features built into software during development may sometimes be left in place when the software is released into production, effectively acting as backdoors.
Spam 📧🚫📢
Spam is different from software-based threats because it is not software that gets installed on your computer. Instead, spam refers to the flood of unsolicited electronic messages sent to users. Most spam arrives via email, but it can also appear in instant messages, text messages, online classifieds, on smartphones, in internet forums, and in message groups.
Most spam consists of advertisements, and it costs spammers very little to send it. All they need is a program to generate spam—called a spam bot—and large email lists. While spammers incur almost no cost, internet service providers (ISPs), businesses, and users incur high costs to install and maintain hardware and software to handle the massive volume of spam. It is estimated that over 9 trillion spam messages are sent each year. Clearly, laws that make spam illegal in many regions have had a limited impact.
Real-world analogy:
Spam is like junk flyers stuffed into your mailbox every day. Most are annoying ads, but some are cleverly disguised scams that try to trick you into opening the door to a thief.
While much spam is simply advertising, a large portion is designed to defraud users. These messages often contain links that lead to malicious websites or cause users to download viruses or other malware. Many users know that clicking links from unknown senders is risky, but it still happens—especially when spam emails are made to look like they come from legitimate businesses, your ISP, or even someone in your contact list.
Spam is not limited to email. A person who repeatedly posts the same message in an online forum or discussion group is also considered a spammer. In these cases, the goal is often to disrupt conversations or hijack threads.
The best way to deal with spam that reaches your inbox is to delete it. Most email clients include junk mail or spam filters, and you can mark unwanted messages as spam. Doing so helps ensure that future emails from the same sender are automatically redirected to your junk or spam folder.
Password Cracking 🔑💥🧠
Most of us type in passwords many times a day. Using a username and password has become a standard for accessing computers, websites, and online services. Unfortunately, some people seek unauthorized access to your data, and one common way they try to do so is through password cracking.
Password cracking can take several forms. The simplest method is to try the default password for a device or service, especially if the user never changed it. Another common technique is password reuse—attackers who know your password on one site may try it on others, since many people reuse passwords.
Real-world analogy:
Password cracking is like someone trying different keys on your door—starting with common keys, then keys they’ve seen you use elsewhere, and finally trying every possible key until one works.
Attackers may also guess passwords based on personal information they know about you, such as names, birthdays, pets, or short phrases related to your life. The most powerful method is brute-force, where an automated program tries random character combinations until the correct password is found.
This process is much faster than many people realize. A regular desktop or laptop running password-cracking software can try around 9 billion password combinations per second, meaning an 8-character password with numbers, mixed case, and symbols could be cracked in about five minutes. Specialized password-cracking systems can attempt up to 90 billion combinations per second.
Fortunately, most websites and computer systems limit the number of login attempts, usually locking the account after about five failed tries, which helps protect against brute-force attacks.
Important note: Password-cracking software itself is not illegal and has many legitimate uses. It can help recover lost passwords or be used during security audits to test system strength. However, attempting to access a system you do not own or have permission to test is illegal.
Wrapping Up 🧭
In this article, we explored software-based threats that are designed to hide quietly, monitor activity, and maintain control over systems without being easily detected. Unlike obvious attacks, these threats often operate in the background, giving attackers time to collect data, spread malware, or lock users out of their own systems.
The key takeaway is awareness and prevention. Being cautious about what you install, keeping systems and security software up to date, using strong and unique passwords, and maintaining reliable backups can significantly reduce your risk. Understanding how these threats work is one of the most effective ways to recognize warning signs early and protect your data before serious damage occurs.
This article is part of the Security Concepts & Threats series, which explores the fundamentals of protecting data, people, and devices in a connected world. For the full overview of how modern risks, defenses, and access controls fit together, refer to the main article in this series. 👉 Security Concepts&Threats