What are the most common types of malware, and how would you recognize the symptoms of an infection on a user's workstation?

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Malware is a broad term for any software designed to harm, exploit, or compromise a computer system. Understanding the different types of malware and recognizing infection symptoms helps IT support technicians respond quickly and limit the damage.

A virus is one of the oldest types of malware. It attaches itself to a legitimate file or program and spreads when that file is shared or executed. Viruses require user action to propagate, such as opening an infected email attachment or running a compromised installer. Once activated, a virus can corrupt files, slow down the system, or delete data.

A worm is similar to a virus but does not need user interaction to spread. Worms exploit vulnerabilities in the operating system or network services to replicate themselves across connected machines. A single worm can spread through an entire network within minutes, consuming bandwidth and system resources as it goes.

A trojan, named after the Trojan Horse from Greek mythology, disguises itself as legitimate software. The user installs it thinking they are getting a useful application, but once running, the trojan opens a backdoor that allows attackers to access the system remotely, steal data, or install additional malware.

Ransomware is one of the most disruptive types of malware in modern IT environments. It encrypts the user's files and displays a message demanding payment in exchange for the decryption key. The files become completely inaccessible, and without backups, the data may be permanently lost. Ransomware often spreads through phishing emails or compromised websites.

Spyware operates silently in the background, monitoring user activity without their knowledge. It can capture keystrokes, record browsing history, steal login credentials, and transmit this information to the attacker. Spyware often arrives bundled with free software downloads.

Adware is a less harmful but still disruptive type of malware that displays unwanted advertisements, pop-ups, or browser redirects. While not always malicious in intent, adware can degrade system performance and sometimes serve as a delivery mechanism for more dangerous malware.

Recognizing an infection on a user's workstation involves watching for several common symptoms. The computer running noticeably slower than usual, unexpected pop-up windows or browser redirects, unfamiliar programs appearing in the startup list or system tray, the antivirus software being disabled without explanation, files being modified, encrypted, or deleted unexpectedly, and unusual network activity in Task Manager are all warning signs.

When you suspect an infection, follow your organization's incident response procedures. Disconnect the machine from the network to prevent the malware from spreading, run a full antivirus scan, and escalate to the security team if the infection is confirmed or if the antivirus cannot remove it. Document the symptoms, the time they were first noticed, and any actions the user took before the infection appeared.