Antivirus software blocks files from opening primarily to protect your computer from malicious software, commonly known as malware. It analyzes files using signature-based detection (comparing files against a database of known threats) and heuristic analysis (identifying suspicious behavior patterns). When a file matches these malicious indicators or exhibits behaviors associated with harm—such as attempting unauthorized changes to system files—the antivirus proactively stops it from executing to prevent infection. This is a core security measure exercising caution before damage can occur.

For instance, if the file is a known type of ransomware like Cryptolocker, the antivirus will detect its signature and prevent it from opening to encrypt your files. Similarly, a seemingly harmless downloaded document might contain concealed malicious macros designed to run harmful scripts upon opening; heuristic analysis identifies this suspicious activity and blocks the file launch. This prevention is common in everyday environments like receiving email attachments or downloading software from the web.

The main advantage is enhanced protection against data theft, system damage, and cyberattacks. However, a significant limitation is the occurrence of false positives, where legitimate files (like harmless scripts or specialized software tools) are mistakenly blocked, potentially disrupting workflows. Vendors continuously refine detection methods to improve accuracy. Regular antivirus updates are crucial for recognizing the latest threats and minimizing false alerts.