Glossary
fullword
The fullword modifier requires a YARA string to be delimited by non-alphanumeric characters, so it is not matched inside longer words.
With fullword, $a = "evil" fullword matches evil.exe or (evil) but not devil or evilcorp. The characters just before and after the match must not be letters or digits (or the match must be at the start or end of the data).
It reduces false positives for short, common words. It is not available for hex strings and cannot be combined with base64.