Antivirus software scans all files accessed on your computer, including saved files, to detect and prevent malicious threats. Files are blocked when the antivirus identifies code or behavior patterns matching known malware signatures or heuristic analysis flags that indicate suspicious activity. While designed to block threats, this sometimes affects legitimate files if they share characteristics with malicious programs, known as a false positive.

For example, a user saving a downloaded report in PDF format might find it blocked if the file contains unusual scripting elements that trigger heuristics. Similarly, executable files saved from programming projects or modded game files are frequently blocked because antivirus solutions often categorize unsigned or uncommon code as potentially dangerous. This occurs across most antivirus platforms like Windows Defender, Norton, or McAfee.

Blocking prevents malware execution, protecting systems from infection or data theft. However, false positives cause frustration by interrupting legitimate workflows or corrupting files. Users can mitigate this by submitting blocked files to their antivirus vendor for whitelisting. Future improvements include better AI-based context analysis to reduce false alarms without compromising security.