## Facts

- Hilgraeve owned U.S. Patent No. 5,319,776 covering “in transit” virus detection that screens transferred data “prior to storage” and automatically blocks storage if viral sequences are detected.
- The asserted claims included a method claim requiring “receiving and screening the transferred digital data prior to storage on the destination storage medium” and “automatically inhibiting” storage of infected data, and a system claim reciting analogous “means” limitations.
- During prosecution, after initial rejections, Hilgraeve amended the claims and added limitations emphasizing “prior to storage” screening and automatic inhibition of storage to distinguish prior art.
- Hilgraeve accused McAfee’s VirusScan antivirus product of infringing the asserted claims, both literally and under the doctrine of equivalents.
- McAfee argued VirusScan scanned only after data had been stored, so it did not satisfy the “prior to storage” / “in transit” and automatic inhibition limitations as claimed.
- The district court granted summary judgment of no literal infringement and held prosecution history estoppel barred infringement under the doctrine of equivalents based on the narrowing prosecution amendments.

## Issues

1. Whether summary judgment of no literal infringement was proper where the parties disputed how VirusScan interacts with the operating system and whether scanning occurs “prior to storage” as required by the claims.
2. Whether prosecution history estoppel barred Hilgraeve from asserting the doctrine of equivalents for limitations added or emphasized during prosecution concerning “in transit” screening and automatic inhibition of storage.

## Decision

- The Federal Circuit vacated the summary judgment of no literal infringement and remanded because the record contained genuine disputes of material fact about VirusScan’s operation relative to the “prior to storage” / “in transit” limitations.
- The Federal Circuit affirmed that prosecution history estoppel barred Hilgraeve from relying on the doctrine of equivalents for the narrowed limitations tied to automatic inhibition of storage (and related “in transit” aspects).
- Disposition: affirmed in part, vacated in part, and remanded.

## Legal Principles

- Summary judgment of noninfringement is improper when a genuine dispute of material fact exists regarding the accused product’s operation and whether it meets claim limitations.
- When a patentee narrows claim scope by amendment for a substantial reason related to patentability (including to overcome prior art), prosecution history estoppel prevents recapturing surrendered subject matter through the doctrine of equivalents.
- Claim language requiring virus screening “prior to storage” and “automatic” inhibition of storage is treated as a narrowing limitation, particularly when inserted or emphasized during prosecution to secure allowance.

## Conclusion

The Federal Circuit required further proceedings on literal infringement because factual disputes remained about whether VirusScan screened data before storage, but it held Hilgraeve could not use the doctrine of equivalents to extend the claims to systems that scan after storage or do not automatically prevent storage, because those alternatives were surrendered during prosecution.


Hilgraeve Corp. v. McAfee Assocs., Inc., 224 F.3d 1349 (Fed. Cir. 2000)