rkhunter binary package in Ubuntu Focal amd64

 Rootkit Hunter scans systems for known and unknown rootkits,
 backdoors, sniffers and exploits.
 .
 It checks for:
  - SHA256 hash changes;
  - files commonly created by rootkits;
  - executables with anomalous file permissions;
  - suspicious strings in kernel modules;
  - hidden files in system directories;
 and can optionally scan within files.
 .
 Using rkhunter alone does not guarantee that a system is not
 compromised. Running additional tests, such as chkrootkit, is
 recommended.

Source package