Disclosed are systems, methods and computer program products for adaptively modifying antivirus databases. In one example, a system stores in an antivirus database a list of file types and antivirus records for different file types. When the system receives files for performing antivirus analysis, it retrieves from the database the list of file types and uses it to determine file types of the received files. The system then retrieves from the database antivirus lists for the determined file types and uses them to perform antivirus analysis of the files. The system then identifies files with an unknown file type and attempts to determine the file type of these files. The system then updates the antivirus database by (i) adding to the list of file types a new file type corresponding to said unknown file type, and (ii) adding a new empty antivirus list corresponding to said unknown file type.