diff --git a/manual/add-note.php b/manual/add-note.php
index 1398e5d006..ef9d63d509 100644
--- a/manual/add-note.php
+++ b/manual/add-note.php
@@ -1,11 +1,15 @@
 <?php
+
+use phpweb\Spam\Challenge;
+
 $ip_spam_lookup_url = 'http://www.dnsbl.info/dnsbl-database-check.php?IP=';
 
 $_SERVER['BASE_PAGE'] = 'manual/add-note.php';
+
+require_once __DIR__ . '/../autoload.php';
 include_once __DIR__ . '/../include/prepend.inc';
 include_once __DIR__ . '/../include/posttohost.inc';
 include_once __DIR__ . '/../include/shared-manual.inc';
-include __DIR__ . '/spam_challenge.php';
 
 use phpweb\UserNotes\UserNote;
 
@@ -55,7 +59,7 @@
     }
 
     // SPAM challenge failed
-    elseif (!test_answer($_POST['func'], $_POST['arga'], $_POST['argb'], $_POST['answer'])) {
+    elseif (!Challenge::isValidAnswer($_POST['func'], $_POST['arga'], $_POST['argb'], $_POST['answer'])) {
         $error = 'SPAM challenge failed.';
     }
 
@@ -366,14 +370,14 @@
   </tr>
   <tr>
    <th class="subr"><label for="form-answer">Answer to this simple question (SPAM challenge)</label>:<br>
-   <?php $c = gen_challenge(); echo $c[3]; ?>?</th>
+   <?php $c = Challenge::create(); echo $c->question; ?>?</th>
    <td><input id="form-answer" type="text" name="answer" size="60" maxlength="10" required> (Example: nine)</td>
   </tr>
   <tr>
    <th colspan="2">
-    <input type="hidden" name="func" value="<?php echo $c[0]; ?>">
-    <input type="hidden" name="arga" value="<?php echo $c[1]; ?>">
-    <input type="hidden" name="argb" value="<?php echo $c[2]; ?>">
+    <input type="hidden" name="func" value="<?php echo $c->function; ?>">
+    <input type="hidden" name="arga" value="<?php echo $c->argumentOne; ?>">
+    <input type="hidden" name="argb" value="<?php echo $c->argumentTwo; ?>">
     <input type="submit" name="action" value="Preview">
     <input type="submit" name="action" value="Add Note">
    </th>
diff --git a/manual/spam_challenge.php b/manual/spam_challenge.php
deleted file mode 100644
index 15bf6a5dd7..0000000000
--- a/manual/spam_challenge.php
+++ /dev/null
@@ -1,66 +0,0 @@
-<?php
-
-// simple and stupid SPAM protection (using little challenges)
-
-const NUMS = ['zero', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine'];
-
-function plus($a, $b) {
-    return $a + $b;
-}
-
-function gen_plus($a) {
-    return mt_rand(0, 9 - $a);
-}
-
-function minus($a, $b) {
-    return $a - $b;
-}
-
-function gen_minus($a) {
-    return mt_rand(0, $a);
-}
-
-function print_infix($name, $a, $b) {
-    return "$a $name $b";
-}
-
-function print_prefix($name, $a, $b) {
-    return "$name($a, $b)";
-}
-
-const CHALLENGES = [
-    // name, print, generator
-    ['max',   'print_prefix'],
-    ['min',   'print_prefix'],
-    ['minus', 'print_infix', 'gen_minus'],
-    ['plus',  'print_infix', 'gen_plus'],
-];
-
-// generate a challenge
-function gen_challenge() {
-    $c = CHALLENGES[mt_rand(0, count(CHALLENGES) - 1)];
-
-    $a = mt_rand(0, 9);
-    $an = NUMS[$a];
-    $b = isset($c[2]) ? $c[2]($a) : mt_rand(0, 9);
-    $bn = NUMS[$b];
-
-    return [$c[0], $an, $bn, $c[1]($c[0], $an, $bn)];
-}
-
-// test an answer for validity
-function test_answer($name, $an, $bn, $answer) {
-    foreach (CHALLENGES as $x) {
-        if ($x[0] === $name) {
-            $c = $x;
-            break;
-        }
-    }
-
-    $a = array_search($an, NUMS, false);
-    $b = array_search($bn, NUMS, false);
-
-    if (empty($c) || $a === false || $b === false) return false;
-
-    return (NUMS[$c[0]($a, $b)] === $answer);
-}
diff --git a/manual/vote-note.php b/manual/vote-note.php
index fa8de7c7e2..4e2a21ce4a 100644
--- a/manual/vote-note.php
+++ b/manual/vote-note.php
@@ -1,9 +1,13 @@
 <?php
+
+use phpweb\Spam\Challenge;
+
 $_SERVER['BASE_PAGE'] = 'manual/vote-note.php';
+
+require_once __DIR__ . '/../autoload.php';
 include_once __DIR__ . '/../include/prepend.inc';
 include_once __DIR__ . '/../include/posttohost.inc';
 include_once __DIR__ . '/../include/shared-manual.inc';
-include_once __DIR__ . '/spam_challenge.php';
 
 // Initialize global variables
 $error = false;
@@ -53,7 +57,7 @@
   }
   if (!empty($_REQUEST['id']) && !empty($_REQUEST['page']) && ($N = manual_notes_load($_REQUEST['page'])) && array_key_exists($_REQUEST['id'], $N) && !empty($_REQUEST['vote']) && ($_REQUEST['vote'] === 'up' || $_REQUEST['vote'] === 'down')) {
     if (!empty($_POST['challenge']) && !empty($_POST['func']) || empty($_POST['arga']) || empty($_POST['argb'])) {
-      if (!test_answer($_POST['func'], $_POST['arga'], $_POST['argb'], $_POST['challenge'])) {
+      if (!Challenge::isValidAnswer($_POST['func'], $_POST['arga'], $_POST['argb'], $_POST['challenge'])) {
         $error = "Incorrect answer! Please try again.";
       }
       else {
@@ -109,13 +113,13 @@
   <div style="background-color: #f5f5ff; border: 1px solid black; padding: 15px; width: 90%; margin: auto;">
    <form action="" method="post">
     <div>
-    <p><label for="form-challenge">Please answer this simple SPAM challenge</label>: <strong><?php $c = gen_challenge(); echo $c[3]; ?></strong>?<br>
+    <p><label for="form-challenge">Please answer this simple SPAM challenge</label>: <strong><?php $c = Challenge::create(); echo $c->question; ?></strong>?<br>
     <input id="form-challenge" type="text" name="challenge" maxlength="10" required> (Example: nine)</p>
     <p><input type="submit" value="Vote" name="votenote"></p>
     </div>
-    <input type="hidden" name="func" value="<?php echo $c[0]; ?>">
-    <input type="hidden" name="arga" value="<?php echo $c[1]; ?>">
-    <input type="hidden" name="argb" value="<?php echo $c[2]; ?>">
+    <input type="hidden" name="func" value="<?php echo $c->function; ?>">
+    <input type="hidden" name="arga" value="<?php echo $c->argumentOne; ?>">
+    <input type="hidden" name="argb" value="<?php echo $c->argumentTwo; ?>">
    </form>
   </div>
  </div>
@@ -158,13 +162,13 @@
   <div style="background-color: #f5f5ff; border: 1px solid black; padding: 15px; width: 90%; margin: auto;">
    <form action="" method="post">
     <div>
-    <p><label for="form-challenge">Please answer this simple SPAM challenge</label>: <strong><?php $c = gen_challenge(); echo $c[3]; ?></strong>?<br>
+    <p><label for="form-challenge">Please answer this simple SPAM challenge</label>: <strong><?php $c = Challenge::create(); echo $c->question; ?></strong>?<br>
     <input id="form-challenge" type="text" name="challenge" maxlength="10" required> (Example: nine)</p>
     <p><input type="submit" value="Vote" name="votenote"></p>
     </div>
-    <input type="hidden" name="func" value="<?php echo $c[0]; ?>">
-    <input type="hidden" name="arga" value="<?php echo $c[1]; ?>">
-    <input type="hidden" name="argb" value="<?php echo $c[2]; ?>">
+    <input type="hidden" name="func" value="<?php echo $c->function; ?>">
+    <input type="hidden" name="arga" value="<?php echo $c->argumentOne; ?>">
+    <input type="hidden" name="argb" value="<?php echo $c->argumentTwo; ?>">
    </form>
   <?php echo $error_div; ?>
   </div>
diff --git a/src/Spam/Challenge.php b/src/Spam/Challenge.php
new file mode 100644
index 0000000000..3a3466990e
--- /dev/null
+++ b/src/Spam/Challenge.php
@@ -0,0 +1,160 @@
+<?php
+
+declare(strict_types=1);
+
+namespace phpweb\Spam;
+
+final readonly class Challenge
+{
+    private const NUMBERS = [
+        0 => 'zero',
+        1 => 'one',
+        2 => 'two',
+        3 => 'three',
+        4 => 'four',
+        5 => 'five',
+        6 => 'six',
+        7 => 'seven',
+        8 => 'eight',
+        9 => 'nine',
+    ];
+
+    private const CHALLENGES = [
+        // name, print, generator
+        'max' => [
+            'max',
+            [
+                self::class,
+                'print_prefix',
+            ],
+        ],
+        'min' => [
+            'min',
+            [
+                self::class,
+                'print_prefix',
+            ],
+        ],
+        'minus' => [
+            [
+                self::class,
+                'minus',
+            ],
+            [
+                self::class,
+                'print_infix',
+            ],
+            [
+                self::class,
+                'gen_minus',
+            ],
+        ],
+        'plus' => [
+            [
+                self::class,
+                'plus',
+            ],
+            [
+                self::class,
+                'print_infix',
+            ],
+            [
+                self::class,
+                'gen_plus',
+            ],
+        ],
+    ];
+
+    private function __construct(
+        public string $function,
+        public string $argumentOne,
+        public string $argumentTwo,
+        public string $question,
+    ) {
+    }
+
+    public static function create(): self
+    {
+        $function = array_rand(self::CHALLENGES);
+
+        $challenge = self::CHALLENGES[$function];
+
+        $a = mt_rand(0, 9);
+        $argumentOne = self::NUMBERS[$a];
+
+        $b = isset($challenge[2]) ? $challenge[2]($a) : mt_rand(0, 9);
+        $argumentTwo = self::NUMBERS[$b];
+
+        $question = $challenge[1](
+            $function,
+            $argumentOne,
+            $argumentTwo,
+        );
+
+        return new self(
+            $function,
+            $argumentOne,
+            $argumentTwo,
+            $question,
+        );
+    }
+
+    public static function isValidAnswer(
+        string $function,
+        string $argumentOne,
+        string $argumentTwo,
+        string $answer,
+    ): bool {
+        if (!array_key_exists($function, self::CHALLENGES)) {
+            return false;
+        }
+
+        $challenge = self::CHALLENGES[$function];
+
+        $a = array_search($argumentOne, self::NUMBERS, true);
+
+        if (!is_int($a)) {
+            return false;
+        }
+
+        $b = array_search($argumentTwo, self::NUMBERS, true);
+
+        if (!is_int($b)) {
+            return false;
+        }
+
+        $expected = self::NUMBERS[$challenge[0]($a, $b)];
+
+        return $expected === $answer;
+    }
+
+    private static function plus(int $a, int $b): int
+    {
+        return $a + $b;
+    }
+
+    private static function gen_plus(int $a): int
+    {
+        return mt_rand(0, 9 - $a);
+    }
+
+    private static function minus(int $a, int $b): int
+    {
+        return $a - $b;
+    }
+
+    private static function gen_minus(int $a): int
+    {
+        return mt_rand(0, $a);
+    }
+
+    private static function print_infix(string $name, string $a, string $b): string
+    {
+        return "$a $name $b";
+    }
+
+    private static function print_prefix(string $name, string $a, string $b): string
+    {
+        return "$name($a, $b)";
+    }
+}
diff --git a/tests/test-answer.phpt b/tests/Spam/Challenge/is-valid-answer.phpt
similarity index 94%
rename from tests/test-answer.phpt
rename to tests/Spam/Challenge/is-valid-answer.phpt
index 235d68cd76..e948e166be 100644
--- a/tests/test-answer.phpt
+++ b/tests/Spam/Challenge/is-valid-answer.phpt
@@ -1,9 +1,13 @@
 --TEST--
-test_answer() returns true when answer to spam challenge is valid
+Challenge::isValidAnswer() returns true when answer to spam challenge is valid
 --FILE--
 <?php
 
-require_once __DIR__ . '/../manual/spam_challenge.php';
+declare(strict_types=1);
+
+use phpweb\Spam\Challenge;
+
+require_once __DIR__ . '/../../../src/autoload.php';
 
 $answers = [
     [
@@ -73,7 +77,7 @@ $answers = [
 ];
 
 $results = array_map(static function (array $answer): array {
-    $answer['isValid'] = test_answer(
+    $answer['isValid'] = Challenge::isValidAnswer(
         $answer['function'],
         $answer['argumentOne'],
         $answer['argumentTwo'],
diff --git a/tests/gen-challenge.phpt b/tests/Spam/Challenge/random.phpt
similarity index 91%
rename from tests/gen-challenge.phpt
rename to tests/Spam/Challenge/random.phpt
index 714985c46c..cddc84daa0 100644
--- a/tests/gen-challenge.phpt
+++ b/tests/Spam/Challenge/random.phpt
@@ -1,20 +1,24 @@
 --TEST--
-gen_challenge() generates a spam challenge
+Challenge::random() generates a spam challenge
 --FILE--
 <?php
 
-require_once __DIR__ . '/../manual/spam_challenge.php';
+declare(strict_types=1);
+
+use phpweb\Spam\Challenge;
+
+require_once __DIR__ . '/../../../src/autoload.php';
 
 mt_srand(9001);
 
 $challenges = array_map(static function (): array {
-    [$function, $argumentOne, $argumentTwo, $question] = gen_challenge();
+    $challenge = Challenge::create();
 
     return [
-        'function' => $function,
-        'argumentOne' => $argumentOne,
-        'argumentTwo' => $argumentTwo,
-        'question' => $question,
+        'function' => $challenge->function,
+        'argumentOne' => $challenge->argumentOne,
+        'argumentTwo' => $challenge->argumentTwo,
+        'question' => $challenge->question,
     ];
 }, range(1, 20));