Prior Narrow Definition Does Not (Necessarily) Limit Claim Scope in Family Member

Finjan LLC v. ESET LLC, --- F.4th --- (Fed. Cir. 2022)

Finjan's patents claim a system for checking downloadable files for security concerns.  Back in 1996 when Finjan filed its original provisional application, the focus was on applets or other small downloadable programs.  But downloadables today are much bulkier.  Here, the claims require a number of operations on "a downloadable" and the parties have debated throughout the litigation how to construe that term.

The district court's approach was a bit convoluted.

• Construction: The district court first narrowly construed the term as limited only to "small downloadables." Although the asserted patents do not appears to require smallness, the patents do incorporate-by-reference a family member that particularly defines downloadable as “applets” and as “small executable or interpretable application program[s] which [are] downloaded."
• Invalidation: Later, the district court reviewed that construction and concluded that the term "small" is a term of degree without any limiting theory and therefor is invalid as indefinite.