Early online antiviruses were reactive. They could only detect infections after they took place. Moreover, the first antivirus programs identified viruses by the relatively primitive technique of looking for their signature characteristics.
For example, they might know there's a virus with a file name like “PCdestroy,” so if the antivirus software recognized that name, it would stop the threat. However, if the attacker changed the file name, the computer antivirus might not be as effective. While early antivirus software could also recognize specific digital fingerprints or patterns, such as code sequences in network traffic or known harmful instruction sequences, they were often playing catch-up.
For example, they might know there's a virus with a file name like “PCdestroy,” so if the antivirus software recognized that name, it would stop the threat. However, if the attacker changed the file name, the computer antivirus might not be as effective. While early antivirus software could also recognize specific digital fingerprints or patterns, such as code sequences in network traffic or known harmful instruction sequences, they were often playing catch-up.