diff --git a/src/main/java/ch/dissem/bitmessage/server/JabitServerConfig.java b/src/main/java/ch/dissem/bitmessage/server/JabitServerConfig.java
index 205154c..7237e79 100644
--- a/src/main/java/ch/dissem/bitmessage/server/JabitServerConfig.java
+++ b/src/main/java/ch/dissem/bitmessage/server/JabitServerConfig.java
@@ -122,6 +122,7 @@ public class JabitServerConfig {
 
     @Bean
     public Set<BitmessageAddress> admins() {
+        security();
         return Utils.readOrCreateList(
                 ADMIN_LIST,
                 "# Admins can send commands to the server.\n"
diff --git a/src/main/java/ch/dissem/bitmessage/server/ProofOfWorkRequestHandler.java b/src/main/java/ch/dissem/bitmessage/server/ProofOfWorkRequestHandler.java
index eafe85c..ab98b10 100644
--- a/src/main/java/ch/dissem/bitmessage/server/ProofOfWorkRequestHandler.java
+++ b/src/main/java/ch/dissem/bitmessage/server/ProofOfWorkRequestHandler.java
@@ -27,6 +27,7 @@ import ch.dissem.bitmessage.extensions.pow.ProofOfWorkRequest;
 import ch.dissem.bitmessage.ports.CustomCommandHandler;
 import ch.dissem.bitmessage.ports.ProofOfWorkEngine;
 import ch.dissem.bitmessage.server.repository.ServerProofOfWorkRepository;
+import ch.dissem.bitmessage.utils.UnixTime;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -39,6 +40,7 @@ import java.util.stream.Collectors;
 
 import static ch.dissem.bitmessage.extensions.pow.ProofOfWorkRequest.Request.CALCULATING;
 import static ch.dissem.bitmessage.extensions.pow.ProofOfWorkRequest.Request.COMPLETE;
+import static ch.dissem.bitmessage.utils.UnixTime.DAY;
 
 /**
  * @author Christian Basler
@@ -61,6 +63,12 @@ public class ProofOfWorkRequestHandler implements CustomCommandHandler, Internal
                 doMissingProofOfWork();
             }
         }, 15_000); // After 15 seconds
+        new Timer().schedule(new TimerTask() {
+            @Override
+            public void run() {
+                repo.cleanupTasks(7 * DAY);
+            }
+        }, 60_000, DAY * 1000); // First time after 1 minute, then daily
     }
 
     public void doMissingProofOfWork() {
@@ -77,11 +85,12 @@ public class ProofOfWorkRequestHandler implements CustomCommandHandler, Internal
             CryptoCustomMessage<ProofOfWorkRequest> cryptoMessage = CryptoCustomMessage.read(message,
                     ProofOfWorkRequest::read);
             ProofOfWorkRequest request = decrypt(cryptoMessage);
-            if (request == null)
+            if (request == null) {
                 return CustomMessage.error(
                         "Unknown sender. Please ask the server's administrator to add you as a client. " +
                                 "For this he'll need your identity."
                 );
+            }
             switch (request.getRequest()) {
                 case CALCULATE:
                     if (!repo.hasTask(request.getInitialHash())) {
diff --git a/src/main/java/ch/dissem/bitmessage/server/repository/ServerProofOfWorkRepository.java b/src/main/java/ch/dissem/bitmessage/server/repository/ServerProofOfWorkRepository.java
index e37e200..c4af9b2 100644
--- a/src/main/java/ch/dissem/bitmessage/server/repository/ServerProofOfWorkRepository.java
+++ b/src/main/java/ch/dissem/bitmessage/server/repository/ServerProofOfWorkRepository.java
@@ -19,6 +19,7 @@ package ch.dissem.bitmessage.server.repository;
 import ch.dissem.bitmessage.extensions.pow.ProofOfWorkRequest;
 import ch.dissem.bitmessage.repository.JdbcConfig;
 import ch.dissem.bitmessage.repository.JdbcHelper;
+import ch.dissem.bitmessage.utils.UnixTime;
 
 import java.sql.Connection;
 import java.sql.PreparedStatement;
@@ -46,10 +47,11 @@ public class ServerProofOfWorkRepository extends JdbcHelper {
     public void storeTask(ProofOfWorkRequest request) {
         try (Connection connection = config.getConnection()) {
             PreparedStatement ps = connection.prepareStatement(
-                    "INSERT INTO ProofOfWorkTask (initial_hash, client, target) VALUES (?, ?, ?)");
+                    "INSERT INTO ProofOfWorkTask (initial_hash, client, target, timestamp) VALUES (?, ?, ?, ?)");
             ps.setBytes(1, request.getInitialHash());
             ps.setString(2, request.getSender().getAddress());
             ps.setBytes(3, request.getData());
+            ps.setLong(4, UnixTime.now());
             ps.executeUpdate();
         } catch (SQLException e) {
             throw new RuntimeException(e);
@@ -112,6 +114,17 @@ public class ServerProofOfWorkRepository extends JdbcHelper {
         }
     }
 
+    public void cleanupTasks(long ageInSeconds) {
+        try (Connection connection = config.getConnection()) {
+            PreparedStatement ps = connection.prepareStatement(
+                    "DELETE FROM ProofOfWorkTask WHERE timestamp < ?");
+            ps.setLong(1, UnixTime.now(-ageInSeconds));
+            ps.executeUpdate();
+        } catch (SQLException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
     public static class Task {
         public final byte[] initialHash;
         public final byte[] target;
diff --git a/src/main/resources/db/migration/V1.2.1__ProofOfWorkTask.sql b/src/main/resources/db/migration/V1.2.1__ProofOfWorkTask.sql
index 40d3135..0561d9d 100644
--- a/src/main/resources/db/migration/V1.2.1__ProofOfWorkTask.sql
+++ b/src/main/resources/db/migration/V1.2.1__ProofOfWorkTask.sql
@@ -1,7 +1,7 @@
 CREATE TABLE ProofOfWorkTask (
-  initial_hash BINARY(64) NOT NULL PRIMARY KEY,
-  client       VARCHAR(40)   NOT NULL,
+  initial_hash BINARY(64)  NOT NULL PRIMARY KEY,
+  client       VARCHAR(40) NOT NULL,
   target       BINARY(32),
   nonce        BINARY(8),
-  status       VARCHAR(20),
+  timestamp    BIGINT      NOT NULL,
 );
\ No newline at end of file