You will still have to download the update file from the internet, but you can always use or borrow somebody else laptop with internet connection which can be used to download the update and then install it on other computers.
For example, the most popular antivirus that I have seen is Avast (free version).
Antivirus and antispyware are reliable only if they are updated regularly.
Note that most of current anti-virus software updates automatically via the Internet.
Many times, some clients argue with me that it is impossible for their system to be infected because they have an antivirus installed.
Updating your antivirus software doesn’t mean shelling out for a whole new software package.
Most updates only involve installing the latest virus database definitions, and this can be a reasonably quick process.
Here's how to do this with the most common antivirus software.
You can automatically check for Anti-Virus signature updates from Cisco’s signature server every 24 hours or to manually check for Anti-Virus signature updates at any time by clicking Update.