Jaybird does not have a virus in it. I also downloaded the files from https://www.firebirdsql.org/en/jdbc-driver/ but don't get any warning from Windows Defender.
It seems to me that it is either a false positive, or your machine is already infected with something that modifies files on download/open. Consider comparing the hashes shown below with the one of your download.
You can get the (SHA256) hash using PowerShell as:
Get-FileHash Jaybird-3.0.4-JDK_1.8.zip
Output on my machine for both:
Algorithm Hash Path
--------- ---- ----
SHA256 FDBE76C72C21001520BAE8E926F9FDAA227F1B7918660A71283D5D9B0E4E463F D:\install\Jaybird-3.0.4-JDK_1.7.zip
SHA256 86D2C6BB28DE93A8D239A3EC49BF1ED9A29082AC17C899FD801A063C270ADD2A D:\install\Jaybird-3.0.4-JDK_1.8.zip
As Windows Defender on my machine reports no problems, make sure you are using the latest version (I just updated the definitions to 1.267.1375.0 of today).
I also submitted the downloads to https://virusdesk.kaspersky.com/ without anything found:
File Jaybird-3.0.4-JDK_1.7.zip is safe.
The file is safe to keep, use and send.
Scan result
File is safe
File size 9.56 MB
File type ARC/ZIP
Scan date May 15 2018 11:18:31
Databases release date May 15 2018 08:37:28 UTC
MD5 e18897cf9d2fac831879d3d1e49b26be
SHA1 15a53c3408954dd8b9ca976e5fe5f9adaf2e5dfa
SHA256 fdbe76c72c21001520bae8e926f9fdaa227f1b7918660a71283d5d9b0e4e463f
and
File Jaybird-3.0.4-JDK_1.8.zip is safe.
The file is safe to keep, use and send.
Scan result
File is safe
File size 9.84 MB
File type ARC/ZIP
Scan date May 15 2018 11:22:06
Databases release date May 15 2018 08:37:28 UTC
MD5 3f2dd2328e20d83fcf862e78a02eab43
SHA1 cfd6b93175758c7b282af6e5eddf8e7d88ba4ae1
SHA256 86d2c6bb28de93a8d239a3ec49bf1ed9a29082ac17c899fd801a063c270add2a
I also submitted the files to https://virusscan.jotti.org (as suggested by Arioch'The) and none of the 16 scanners used by that site reported problems, see this scan report.
Disclaimer: I maintain Jaybird and created the build.