diff --git a/packaging/systemd/hound-defs-refresh.service b/packaging/systemd/hound-defs-refresh.service
new file mode 100644
index 0000000..385c25b
--- /dev/null
+++ b/packaging/systemd/hound-defs-refresh.service
@@ -0,0 +1,23 @@
+[Unit]
+Description=Rebuild and publish the Hound definition feed
+Documentation=https://houndav.com
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=oneshot
+User=anon
+# Runs as the publisher, not as root: it needs the signing key and write
+# access to the published directory, and nothing else. A build pipeline that
+# runs as root to write a web directory is a larger target than the thing it
+# protects.
+WorkingDirectory=/home/anon/agents/hound/antivirus
+ExecStart=/home/anon/agents/hound/antivirus/tools/refresh-definitions.sh
+# The OSV exports total a few hundred MB and npm alone is a quarter of a
+# million records; a slow morning should not look like a hang.
+TimeoutStartSec=45min
+Nice=10
+IOSchedulingClass=idle
+
+[Install]
+WantedBy=multi-user.target
diff --git a/packaging/systemd/hound-defs-refresh.timer b/packaging/systemd/hound-defs-refresh.timer
new file mode 100644
index 0000000..a71d2ff
--- /dev/null
+++ b/packaging/systemd/hound-defs-refresh.timer
@@ -0,0 +1,17 @@
+[Unit]
+Description=Refresh the Hound definition feed daily
+Documentation=https://houndav.com
+
+[Timer]
+# OSV rebuilds its exports daily. Early UTC means the feed is current before
+# most of the working day starts, wherever the user is.
+OnCalendar=*-*-* 05:20:00 UTC
+# A machine that was off at 05:20 still gets a rebuild rather than silently
+# skipping a day — which is the failure that produces a stale feed nobody
+# notices.
+Persistent=true
+# Spread the load if this ever runs on more than one builder.
+RandomizedDelaySec=20min
+
+[Install]
+WantedBy=timers.target
diff --git a/tools/refresh-definitions.sh b/tools/refresh-definitions.sh
new file mode 100755
index 0000000..5efa733
--- /dev/null
+++ b/tools/refresh-definitions.sh
@@ -0,0 +1,116 @@
+#!/usr/bin/env bash
+#
+# Rebuild the definition feed from OSV and publish it.
+#
+# The client-side update machinery is only worth having if the source it
+# points at actually moves. Everything below already existed as separate
+# manual steps; this is the thing that runs them on a schedule.
+#
+# Publishing is atomic per pack: each is written to a temporary name in the
+# destination directory and renamed into place, so an agent fetching mid-run
+# never sees a half-written pack. index.json is written last, because it is
+# what tells an agent a pack exists — writing it first would advertise files
+# that are not there yet.
+#
+# Old packs are kept. An agent that has not checked in for a while still has
+# a URL that resolves, and disk is cheaper than a failed update.
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+KEY="${HOUND_DEFS_KEY:-$HOME/agents/hound/.secrets/defs-signing.key}"
+DEST="${HOUND_DEFS_DIR:-/srv/houndav/defs}"
+WORK="${HOUND_DEFS_WORK:-/var/tmp/hound-defs}"
+VERSION="$(date -u +%Y.%m.%d)"
+
+log() { printf '%s %s\n' "$(date -u +%H:%M:%S)" "$*"; }
+
+[ -f "$KEY" ] || { echo "no signing key at $KEY" >&2; exit 1; }
+[ -d "$DEST" ] || { echo "no destination directory $DEST" >&2; exit 1; }
+
+mkdir -p "$WORK"
+log "refreshing definitions for $VERSION"
+
+# The OSV exports are large and change slowly; a failure to fetch one
+# ecosystem must not discard the others.
+python3 "$ROOT/tools/ingest-osv.py" "$WORK"
+
+BUILDER="$ROOT/target/release/examples/build-pack"
+if [ ! -x "$BUILDER" ]; then
+  log "building the pack builder"
+  ( cd "$ROOT" && cargo build --release -p hound-defs --example build-pack )
+fi
+
+# Outside $WORK on purpose: the loop below treats every directory in $WORK as
+# an ecosystem, and a staging directory in there gets built into a pack named
+# after the mktemp suffix. Which is exactly what happened the first time.
+STAGE="$(mktemp -d "${TMPDIR:-/var/tmp}/hound-defs-stage.XXXXXX")"
+trap 'rm -rf "$STAGE"' EXIT
+
+published=0
+for dir in "$WORK"/*/; do
+  eco="$(basename "$dir")"
+  # Lower-case, and '.' is not wanted in a filename component.
+  name="$(echo "$eco" | tr '[:upper:]' '[:lower:]' | tr '.' '-')"
+  case "$name" in
+    stage*|.*) log "$eco: not an ecosystem, skipping"; continue ;;
+  esac
+  count="$(find "$dir" -maxdepth 1 -name '*.json' | wc -l)"
+  if [ "$count" -eq 0 ]; then
+    log "$eco: no malicious records, skipping"
+    continue
+  fi
+  pack="$STAGE/${name}-${VERSION}.pack"
+  if "$BUILDER" "$dir" "$pack" "$KEY" "$VERSION" >/dev/null 2>&1; then
+    log "$eco: built $(basename "$pack") from $count record(s)"
+    published=$((published + 1))
+  else
+    log "$eco: BUILD FAILED — keeping the previous pack"
+  fi
+done
+
+if [ "$published" -eq 0 ]; then
+  # Never publish an empty feed. An agent that installs it would report a
+  # clean machine with no indicators loaded, which is worse than one that
+  # keeps yesterday's.
+  log "nothing built; leaving the published feed untouched"
+  exit 1
+fi
+
+# Packs first, then the index that advertises them.
+for pack in "$STAGE"/*.pack; do
+  base="$(basename "$pack")"
+  cp "$pack" "$DEST/.$base.tmp"
+  chmod 644 "$DEST/.$base.tmp"
+  mv -f "$DEST/.$base.tmp" "$DEST/$base"
+done
+
+python3 - "$DEST" "$VERSION" <<'PY'
+import hashlib, json, os, sys
+dest, version = sys.argv[1], sys.argv[2]
+packs = []
+# One pack per ecosystem: the newest. Older ones stay on disk so existing
+# URLs keep resolving, but the index only ever advertises current data.
+newest = {}
+for f in sorted(os.listdir(dest)):
+    if not f.endswith(".pack"):
+        continue
+    eco = f.rsplit("-", 1)[0]
+    newest[eco] = f
+for eco, f in sorted(newest.items()):
+    p = os.path.join(dest, f)
+    packs.append({
+        "file": f,
+        "sha256": hashlib.sha256(open(p, "rb").read()).hexdigest(),
+        "size": os.path.getsize(p),
+        "version": f.rsplit("-", 1)[1][:-5],
+    })
+tmp = os.path.join(dest, ".index.json.tmp")
+with open(tmp, "w") as fh:
+    json.dump({"packs": packs}, fh, indent=2)
+    fh.write("\n")
+os.chmod(tmp, 0o644)
+os.replace(tmp, os.path.join(dest, "index.json"))
+print(f"index.json lists {len(packs)} pack(s)")
+PY
+
+log "published $published pack(s) for $VERSION"