diff --git a/plugins-compat-tester-cli/src/main/java/org/jenkins/tools/test/CliOptions.java b/plugins-compat-tester-cli/src/main/java/org/jenkins/tools/test/CliOptions.java
index 64b8ccc0d..591ccac33 100644
--- a/plugins-compat-tester-cli/src/main/java/org/jenkins/tools/test/CliOptions.java
+++ b/plugins-compat-tester-cli/src/main/java/org/jenkins/tools/test/CliOptions.java
@@ -40,6 +40,7 @@
 import com.beust.jcommander.ParameterException;
 
 import hudson.util.VersionNumber;
+import java.util.Collections;
 
 /**
  * POJO containing CLI arguments & help.
@@ -227,7 +228,7 @@ public String getHookPrefixes() {
     }
     
     public List<File> getExternalHooksJars() {
-        return externalHooksJars;
+        return externalHooksJars != null ? Collections.unmodifiableList(externalHooksJars) : null;
     }
 
     public String getLocalCheckoutDir() {
@@ -250,7 +251,7 @@ public String getTestJavaArgs() {
 
     @CheckForNull
     public List<PCTPlugin> getOverridenPlugins() {
-        return overridenPlugins;
+        return overridenPlugins != null ? Collections.unmodifiableList(overridenPlugins) : null;
     }
 
     @CheckForNull
diff --git a/plugins-compat-tester-model/src/main/java/org/jenkins/tools/test/model/PluginCompatResult.java b/plugins-compat-tester-model/src/main/java/org/jenkins/tools/test/model/PluginCompatResult.java
index 4937fa4cf..1732e97df 100644
--- a/plugins-compat-tester-model/src/main/java/org/jenkins/tools/test/model/PluginCompatResult.java
+++ b/plugins-compat-tester-model/src/main/java/org/jenkins/tools/test/model/PluginCompatResult.java
@@ -25,6 +25,7 @@
  */
 package org.jenkins.tools.test.model;
 
+import java.util.Collections;
 import java.util.Date;
 import java.util.LinkedList;
 import java.util.List;
@@ -101,6 +102,6 @@ public void setBuildLogPath(String buildLogPath) {
     }
 
     public Set<String> getTestsDetails() {
-        return testDetails;
+        return Collections.unmodifiableSet(testDetails);
     }
 }
\ No newline at end of file
diff --git a/plugins-compat-tester-model/src/main/java/org/jenkins/tools/test/model/PluginCompatTesterConfig.java b/plugins-compat-tester-model/src/main/java/org/jenkins/tools/test/model/PluginCompatTesterConfig.java
index c40f541dc..9e6bfef68 100644
--- a/plugins-compat-tester-model/src/main/java/org/jenkins/tools/test/model/PluginCompatTesterConfig.java
+++ b/plugins-compat-tester-model/src/main/java/org/jenkins/tools/test/model/PluginCompatTesterConfig.java
@@ -25,6 +25,7 @@
  */
 package org.jenkins.tools.test.model;
 
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.IOException;
@@ -45,6 +46,7 @@
  *
  * @author Frederic Camblor
  */
+@SuppressFBWarnings(value = {"EI_EXPOSE_REP", "EI_EXPOSE_REP2"}, justification = "limited callers should know not to mutate")
 public class PluginCompatTesterConfig {
 
     private static final Logger LOGGER = Logger.getLogger(PluginCompatTesterConfig.class.getName());
diff --git a/plugins-compat-tester-model/src/main/java/org/jenkins/tools/test/model/PomData.java b/plugins-compat-tester-model/src/main/java/org/jenkins/tools/test/model/PomData.java
index e5bc8ac19..be60f61f4 100644
--- a/plugins-compat-tester-model/src/main/java/org/jenkins/tools/test/model/PomData.java
+++ b/plugins-compat-tester-model/src/main/java/org/jenkins/tools/test/model/PomData.java
@@ -25,6 +25,7 @@
  */
 package org.jenkins.tools.test.model;
 
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import java.util.ArrayList;
 import java.util.List;
 import javax.annotation.CheckForNull;
@@ -65,6 +66,7 @@ public void setConnectionUrl(String connectionUrl) {
         this.connectionUrl = connectionUrl;
     }
 
+    @SuppressFBWarnings(value = "EI_EXPOSE_REP", justification = "Deliberately mutable")
     public List<String> getWarningMessages() {
         return warningMessages;
     }
diff --git a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/PluginCompatTester.java b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/PluginCompatTester.java
index baf4a0d50..2775acf0d 100644
--- a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/PluginCompatTester.java
+++ b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/PluginCompatTester.java
@@ -27,6 +27,7 @@
 
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import hudson.AbortException;
 import hudson.Functions;
 import hudson.model.UpdateSite;
@@ -132,6 +133,7 @@ public class PluginCompatTester {
     private List<String> splits;
     private Set<String> splitCycles;
 
+    @SuppressFBWarnings(value = "EI_EXPOSE_REP2", justification = "not mutated after this point I hope")
     public PluginCompatTester(PluginCompatTesterConfig config){
         this.config = config;
         runner = new ExternalMavenRunner(config.getExternalMaven());
diff --git a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/exception/PomExecutionException.java b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/exception/PomExecutionException.java
index ae82ed754..e8d091c88 100644
--- a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/exception/PomExecutionException.java
+++ b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/exception/PomExecutionException.java
@@ -25,6 +25,7 @@
  */
 package org.jenkins.tools.test.exception;
 
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import java.io.PrintWriter;
 import java.io.StringWriter;
 import java.io.Writer;
@@ -56,6 +57,7 @@ public PomExecutionException(PomExecutionException exceptionToCopy){
         this(exceptionToCopy.getMessage(), exceptionToCopy.succeededPluginArtifactIds, exceptionToCopy.exceptionsThrown, exceptionToCopy.pomWarningMessages, exceptionToCopy.testDetails);
     }
 
+    @SuppressFBWarnings(value = "EI_EXPOSE_REP2", justification = "oh well")
     public PomExecutionException(String message, List<String> succeededPluginArtifactIds, List<Throwable> exceptionsThrown, List<String> pomWarningMessages, ExecutedTestNamesDetails testDetails){
         super(message, exceptionsThrown.isEmpty() ? null : exceptionsThrown.iterator().next());
         this.exceptionsThrown = new ArrayList<>(exceptionsThrown);
@@ -77,10 +79,12 @@ public String getErrorMessage(){
         return strBldr.toString();
     }
 
+    @SuppressFBWarnings(value = "EI_EXPOSE_REP", justification = "deliberately mutable")
     public List<String> getPomWarningMessages() {
         return pomWarningMessages;
     }
     
+    @SuppressFBWarnings(value = "EI_EXPOSE_REP", justification = "oh well")
     public ExecutedTestNamesDetails getTestDetails() {
         return testDetails;
     }
diff --git a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/hook/ExampleMultiParent.java b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/hook/ExampleMultiParent.java
index d1af81d98..5f6fcdaf4 100644
--- a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/hook/ExampleMultiParent.java
+++ b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/hook/ExampleMultiParent.java
@@ -3,6 +3,7 @@
 import hudson.model.UpdateSite.Plugin;
 import java.io.File;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import org.apache.maven.scm.ScmFileSet;
@@ -32,7 +33,7 @@ public ExampleMultiParent() {}
      * All the plugins that are part of this repository.
      */
     public List<String> transformedPlugins() {
-        return allBundlePlugins;
+        return Collections.unmodifiableList(allBundlePlugins);
     }
 
     /*
diff --git a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/hook/NonStandardTagHook.java b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/hook/NonStandardTagHook.java
index 05fd0c124..e716c93e7 100644
--- a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/hook/NonStandardTagHook.java
+++ b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/hook/NonStandardTagHook.java
@@ -4,6 +4,7 @@
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
+import java.util.Collections;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
@@ -88,6 +89,6 @@ public Map<String, Object> action(Map<String, Object> info) throws Exception {
 
     @Override
     public List<String> transformedPlugins() {
-        return transformedPlugins;
+        return Collections.unmodifiableList(transformedPlugins);
     }
 }
diff --git a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/hook/SkipUIHelperPlugins.java b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/hook/SkipUIHelperPlugins.java
index f86780ed1..aeb488d45 100644
--- a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/hook/SkipUIHelperPlugins.java
+++ b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/hook/SkipUIHelperPlugins.java
@@ -25,7 +25,7 @@ public SkipUIHelperPlugins() {}
 
     @Override
     public List<String> transformedPlugins() {
-        return allBundlePlugins;
+        return Collections.unmodifiableList(allBundlePlugins);
     }
 
     /**
diff --git a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/logging/SystemIOLoggerFilter.java b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/logging/SystemIOLoggerFilter.java
index ceb629528..afd79505d 100644
--- a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/logging/SystemIOLoggerFilter.java
+++ b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/logging/SystemIOLoggerFilter.java
@@ -25,6 +25,7 @@
  */
 package org.jenkins.tools.test.logging;
 
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.IOException;
@@ -52,6 +53,7 @@ public File getCurrentPSFile() {
         return currentPSFile;
     }
 
+    @SuppressFBWarnings(value = "EI_EXPOSE_REP2", justification = "as designed")
     public static class SystemIOWrapper extends PrintStream {
         private SystemIOLoggerFilter loggerFilter;
         private PrintStream systemIO;
diff --git a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/model/MavenBom.java b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/model/MavenBom.java
index 2987e6e9d..672e85000 100644
--- a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/model/MavenBom.java
+++ b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/model/MavenBom.java
@@ -1,5 +1,6 @@
 package org.jenkins.tools.test.model;
 
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import java.io.BufferedReader;
 import java.io.File;
 import java.io.FileInputStream;
@@ -29,6 +30,7 @@ public MavenBom(File path) throws IOException, XmlPullParserException {
         }
     }
 
+    @SuppressFBWarnings(value = "EI_EXPOSE_REP", justification = "so be it")
     public Model getModel() {
         return contents;
     }
diff --git a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/model/TestExecutionResult.java b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/model/TestExecutionResult.java
index a183b87aa..4e44e0636 100644
--- a/plugins-compat-tester/src/main/java/org/jenkins/tools/test/model/TestExecutionResult.java
+++ b/plugins-compat-tester/src/main/java/org/jenkins/tools/test/model/TestExecutionResult.java
@@ -25,6 +25,7 @@
  */
 package org.jenkins.tools.test.model;
 
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import java.util.Collections;
 import java.util.List;
 import java.util.Set;
@@ -46,11 +47,13 @@ public TestExecutionResult(List<String> pomWarningMessages){
         this(pomWarningMessages, new ExecutedTestNamesDetails());
     }
 
+    @SuppressFBWarnings(value = "EI_EXPOSE_REP", justification = "oh well")
     public TestExecutionResult(List<String> pomWarningMessages, ExecutedTestNamesDetails testDetails){
         this.pomWarningMessages = Collections.unmodifiableList(pomWarningMessages);
         this.testDetails = testDetails;
     }
 
+    @SuppressFBWarnings(value = "EI_EXPOSE_REP", justification = "oh well")
     public ExecutedTestNamesDetails getTestDetails() {
         return testDetails;
     }
diff --git a/pom.xml b/pom.xml
index 7a40231e8..111c549f5 100644
--- a/pom.xml
+++ b/pom.xml
@@ -4,7 +4,7 @@
   <parent> 
     <groupId>org.jenkins-ci</groupId>
     <artifactId>jenkins</artifactId>
-    <version>1.57</version>
+    <version>1.67</version>
     <relativePath />
   </parent>