diff --git a/src/app/achievements/__tests__/page.test.tsx b/src/app/achievements/__tests__/page.test.tsx
index 051162b8d..4fbcd58a5 100644
--- a/src/app/achievements/__tests__/page.test.tsx
+++ b/src/app/achievements/__tests__/page.test.tsx
@@ -91,6 +91,38 @@ const mockData = {
       completedAt: null,
       isHidden: false,
     },
+    {
+      id: "hidden-night-owl",
+      metric: "nightOwlCount",
+      category: "hidden",
+      titleKey: "achievements.badges.hiddenNightOwl.title",
+      descriptionKey: "achievements.badges.hiddenNightOwl.description",
+      icon: "Moon",
+      format: "count",
+      target: 1,
+      current: 0,
+      points: 25,
+      unlocked: false,
+      progressPercent: 0,
+      completedAt: null,
+      isHidden: true,
+    },
+    {
+      id: "hidden-doctor-pdf",
+      metric: "doctorPdfCount",
+      category: "hidden",
+      titleKey: "achievements.badges.hiddenDoctorPdf.title",
+      descriptionKey: "achievements.badges.hiddenDoctorPdf.description",
+      icon: "FileText",
+      format: "count",
+      target: 1,
+      current: 1,
+      points: 35,
+      unlocked: true,
+      progressPercent: 100,
+      completedAt: "2026-04-30T10:00:00.000Z",
+      isHidden: true,
+    },
   ] satisfies AchievementProgress[],
   metrics: {
     totalTakenIntakes: 1,
@@ -144,7 +176,11 @@ beforeEach(() => {
 describe("groupByCategory", () => {
   it("buckets achievements by category and orders unlocked first", () => {
     const grouped = groupByCategory(mockData.achievements);
-    expect(grouped.map((g) => g.category)).toEqual(["medication", "security"]);
+    expect(grouped.map((g) => g.category)).toEqual([
+      "medication",
+      "security",
+      "hidden",
+    ]);
 
     const medication = grouped.find((g) => g.category === "medication");
     expect(medication?.items.map((i) => i.id)).toEqual([
@@ -212,4 +248,36 @@ describe("<AchievementsPage>", () => {
     expect(html).toContain("Konto &amp; Sicherheit");
     expect(html).toContain("Gesperrt"); // German "Locked"
   });
+
+  it("renders a locked hidden achievement as an opaque placeholder", () => {
+    const html = render();
+    // The opaque card renders the placeholder string
+    expect(html).toContain("Hidden achievement");
+    // Critically, the locked hidden achievement's title and description
+    // must NOT leak into the DOM (this is the whole point of "hidden").
+    expect(html).not.toContain("Night owl");
+    expect(html).not.toContain("Logged an entry between 02:00 and 04:00");
+    // And neither does its trigger metric.
+    expect(html).not.toContain("nightOwlCount");
+  });
+
+  it("renders an unlocked hidden achievement with its real title", () => {
+    const html = render();
+    // The unlocked hidden one ("hidden-doctor-pdf") should now reveal
+    // its strings — that's the reward for unlocking.
+    expect(html).toContain("House call");
+  });
+
+  it("flags hidden cards with the achievement-card-hidden data slot", () => {
+    const html = render();
+    expect(html).toContain('data-slot="achievement-card-hidden"');
+  });
+
+  it("hidden category appears under its own localized heading", () => {
+    const html = render();
+    // English label
+    expect(html).toContain(">Hidden<");
+    const htmlDe = render("de");
+    expect(htmlDe).toContain(">Versteckt<");
+  });
 });
diff --git a/src/app/achievements/page.tsx b/src/app/achievements/page.tsx
index fda1590ee..2111c6e80 100644
--- a/src/app/achievements/page.tsx
+++ b/src/app/achievements/page.tsx
@@ -6,17 +6,26 @@ import {
   AlertTriangle,
   Bug,
   CalendarCheck,
+  CalendarDays,
+  FileText,
   Fingerprint,
   Flame,
+  HelpCircle,
   Heart,
   KeyRound,
+  Languages,
   Loader2,
   Lock,
   LogIn,
+  Moon,
   Pill,
+  Scale,
   ShieldCheck,
   SkipForward,
+  Smile,
+  Sparkles,
   Star,
+  Sun,
   Target,
   Trophy,
   type LucideIcon,
@@ -45,6 +54,8 @@ const iconMap: Record<string, LucideIcon> = {
   Activity,
   Flame,
   CalendarCheck,
+  CalendarDays,
+  FileText,
   Pill,
   ShieldCheck,
   Target,
@@ -52,9 +63,15 @@ const iconMap: Record<string, LucideIcon> = {
   Heart,
   KeyRound,
   Fingerprint,
+  Languages,
   LogIn,
   Bug,
   AlertTriangle,
+  Moon,
+  Scale,
+  Smile,
+  Sparkles,
+  Sun,
   SkipForward,
 };
 
@@ -122,6 +139,40 @@ function AchievementCard({ achievement, t }: AchievementCardProps) {
   const Icon = iconMap[achievement.icon] ?? Star;
   const unlocked = achievement.unlocked;
 
+  // v1.4.18 — locked hidden achievements paint an opaque placeholder.
+  // Critically, the actual title / description / metric / target are
+  // never rendered to the DOM so the user can't peek into the source
+  // to learn the trigger. Once unlocked the real strings appear.
+  if (achievement.isHidden && !unlocked) {
+    return (
+      <div
+        data-slot="achievement-card-hidden"
+        aria-label={t("achievements.hiddenCard.ariaLabel")}
+        className="border-border bg-card/40 rounded-xl border p-3 opacity-70"
+      >
+        <div className="mb-2 flex items-start justify-between gap-2">
+          <div className="flex items-center gap-3">
+            <div className="bg-muted text-muted-foreground rounded-lg p-2">
+              <HelpCircle className="h-3.5 w-3.5" />
+            </div>
+            <div className="min-w-0">
+              <h3 className="text-sm font-semibold">
+                {t("achievements.hiddenCard.title")}
+              </h3>
+              <p className="text-muted-foreground line-clamp-2 text-xs">
+                {t("achievements.hiddenCard.description")}
+              </p>
+            </div>
+          </div>
+          <Badge variant="secondary" className="shrink-0">
+            <Lock className="mr-1 h-3 w-3" aria-hidden="true" />
+            {t("achievements.locked")}
+          </Badge>
+        </div>
+      </div>
+    );
+  }
+
   return (
     <div
       data-slot={