Final answer:
The first line of defense against viruses and worms using signatures to match against them is Antivirus software, which is designed to detect and neutralize these threats.
Step-by-step explanation:
The first line of defense against viruses and worms, using signatures or definitions to match against them, is B) Antivirus software. These programs are specifically designed to detect and neutralize malicious software like viruses and worms by comparing their code to a database of known malware signatures. They are constantly updated to recognize new and evolving threats, providing a protective shield against a wide array of digital infections. Antivirus software operates as a vigilant guard, examining files and programs for any suspicious activity or matches to known virus signatures before they can cause harm. While firewalls and intrusion detection systems play important roles in safeguarding against unauthorized access and detecting potential threats, it is the antivirus software that directly deals with the prevention and removal of viruses by using these specific definitions.