QR codes are two-dimensional barcodes that can be scanned by a smartphone or QR code reader app. They are used for various purposes such as product packaging, real estate, and payments. However, they can also make users vulnerable to phishing if fraudulent codes are created. To avoid these risks, users should only scan QR codes from trusted sources, keep software up to date, use reputable antivirus software, and be cautious when entering sensitive information.