Hi Irina,

Malware refers to any type of malicious software that tries to infect a computer or mobile device. Hackers use malware for any number of reasons such as, extracting personal information or passwords, stealing money, or preventing owners from accessing their device. ‘Malware’ is a general term used to refer to a variety of forms of hostile or intrusive software.
It’s not always easy to tell if your computer was compromised or not,because these days cybercriminals are going to great lengths to hide their code and conceal what their programs are doing on an infected computer.
It’s very difficult to provide a list of characteristic symptoms of a infected computer because the same symptoms can also be caused by hardware incompatibilities or system instability,however here are just a few examples that may suggest that your PC has been compromised :

• You may receive the error “Internet Explorer could not display the page” when attempting to access certain websites
• Your web browser (e.g., Microsoft Internet Explorer, Mozilla Firefox, Google Chrome) freezes, hangs or is unresponsive
• Your web browser’s default homepage is changed
• Access to security related websites is blocked
• You get redirected to web pages other than the one you intended to go to
• You receive numerous web-browser popup messages
• Strange or unexpected toolbars appear at the top of your web browser
• Your computer runs slower than usual
• Your computer freezes, hangs or is unresponsive
• There are new icons on your desktop that you do not recognize
• Your computer restarts by itself (but not a restart caused by Windows Updates)
• You see unusual error messages (e.g., messages saying there are missing or corrupt files folders)
• You are unable to access the Control Panel, Task Manager, Registry Editor or Command Prompt.

Malware includes computer viruses, ransomware, worms, trojan horses, rootkits, keyloggers, dialers, spyware, adware, malicious BHOs, rogue security software and other malicious programs; the majority of active malware threats are usually worms or trojans rather than viruses.

To remove a Trojan, Virus, Worm, or other Malware from Windows, follow these steps:

• STEP 1: Use Rkill to terminate suspicious programs
• STEP 2: Use Malwarebytes to remove Trojans, Rootkits, or other Malware
• STEP 3: Use HitmanPro to scan for Browser Hijackers and Adware
• STEP 4: Use Zemana AntiMalware Free to remove Potentially Unwanted Programs
• (OPTIONAL) STEP 5: Double-check for malicious programs with Emsisoft Emergency Kit
• (OPTIONAL) STEP 6: Reset your browser to default settings

I hope this helps.

Regards,
Lokesh