The most common source of adware infections is additional software installed while you thought you were installing something else. Whenever you download a program from the internet, pay close attention to each screen of the installer, especially if it's free. Be sure to decline any additional offers and double-check each checkbox.  Look for open-source alternatives, which generally will not have any adware in the installer. Avoid download sites like CNet or Tucows, as these will try to get you to use their ad-serving download manager programs. If you're using a Windows computer, you should have an antivirus program running at virtually all times. Windows Defender is usually more than sufficient, but you can use Avast, Bit-Defender, Kaspersky, or other reputable antivirus programs as well. Just make sure that you only have one anti-virus enabled at a time, as they can conflict with each other. See Install an Antivirus for detailed instructions on finding and installing an antivirus program. Too much dust can cause heat to build up inside of your computer. If your computer gets too hot, the components will automatically slow down to try to lower the temperature. Keeping your computer clean and cool can help make sure it's always running at peak efficiency. This is even more important if you have pets or smoke in the house.  You can purchase cans of compressed air or use an air compressor to remove most dust from inside the computer. See Clean a PC for tips on cleaning all of the dust out of your computer. If you stay on top of your installed programs, you can keep your computer bloat-free for a long time. Remove programs once you don't need them anymore, and you'll free up lots of space. You can even keep backups of the installers so that you can quickly install them again in the future without having to re-download the files.

TL;DR in Vietnamese:
Hết sức cẩn thận khi tải chương trình trên Internet. Chạy phần mềm diệt virus có dung lượng nhẹ. Thường xuyên vệ sinh máy tính. Gỡ cài đặt các chương trình khi đã dùng xong.