diff --git a/etc/getdown.pro b/etc/getdown.pro
index a8fb173..aac5920 100644
--- a/etc/getdown.pro
+++ b/etc/getdown.pro
@@ -8,6 +8,7 @@
 -injars dist/getdown.jar(!**/tools/DigesterTask*,!**/tools/Differ*)
 -injars lib/jRegistryKey.jar(!META-INF/*)
 -injars lib/samskivert.jar(!META-INF/*,!**/velocity/**,!**/xml/**)
+-injars lib/commons-codec.jar(!META-INF/*)
 -injars lib/commons-io.jar(!META-INF/*)
 -injars lib/snark.jar(!META-INF/*)
 
diff --git a/lib/LIBS b/lib/LIBS
index ff566c1..e2f70ea 100644
--- a/lib/LIBS
+++ b/lib/LIBS
@@ -1,5 +1,6 @@
 samskivert.jar
 ant.jar
+commons-codec.jar
 commons-io.jar
 javaws.jar
 snark.jar
diff --git a/src/java/com/threerings/getdown/launcher/GetdownApplet.java b/src/java/com/threerings/getdown/launcher/GetdownApplet.java
index 9c4a454..a8220c8 100644
--- a/src/java/com/threerings/getdown/launcher/GetdownApplet.java
+++ b/src/java/com/threerings/getdown/launcher/GetdownApplet.java
@@ -23,6 +23,9 @@ package com.threerings.getdown.launcher;
 import java.awt.Container;
 import java.awt.Image;
 import java.net.URL;
+import java.security.GeneralSecurityException;
+import java.security.Signature;
+import java.security.cert.Certificate;
 
 import javax.swing.JApplet;
 import javax.swing.JPanel;
@@ -32,6 +35,8 @@ import java.io.FileOutputStream;
 import java.io.File;
 import java.io.PrintStream;
 
+import org.apache.commons.codec.binary.Base64;
+
 import com.samskivert.util.RunAnywhere;
 import com.samskivert.util.StringUtil;
 
@@ -46,6 +51,54 @@ public class GetdownApplet extends JApplet
     @Override // documentation inherited
     public void init ()
     {
+        // First off, verify that we are not being hijacked to execute
+        // malicious code in the name of the signer.
+        String appbase = getParameter("appbase");
+        String appname = getParameter("appname");
+        String imgpath = getParameter("bgimage");
+        if (appbase == null) {
+            appbase = "";
+        }
+        if (appname == null) {
+            appname = "";
+        }
+        if (imgpath == null) {
+            imgpath = "";
+        }
+        String params = appbase + appname + imgpath;
+        String signature = getParameter("signature");
+        if (signature == null) {
+            signature = "";
+        }
+
+        Object[] signers = GetdownApplet.class.getSigners();
+        if (signers.length == 0) {
+            _safe = true;
+        }
+        for (Object signer : signers) {
+            if (!_safe && signer instanceof Certificate) {
+                Certificate cert = (Certificate)signer;
+                try {
+                    Signature sig = Signature.getInstance("SHA1withRSA");
+                    sig.initVerify(cert);
+                    Log.info(params);
+                    sig.update(params.getBytes());
+                    byte[] rawsig = Base64.decodeBase64(signature.getBytes());
+                    if (sig.verify(rawsig)) {
+                        _safe = true;
+                    }
+                } catch (GeneralSecurityException gse) {
+                    // ignore the error - the default is to not launch.
+                }
+            }
+        }
+
+        if (!_safe) {
+            Log.warning("Signed getdown invoked on unsigned application; " +
+                "aborting installation.");
+            return;
+        }
+
         // when run from an applet, we install 
         String root;
         if (RunAnywhere.isWindows()) {
@@ -56,7 +109,6 @@ public class GetdownApplet extends JApplet
             root = ".getdown";
         }
 
-        String appname = getParameter("appname");
         String appdir = System.getProperty("user.home") +
             File.separator + root + File.separator + appname;
 
@@ -82,7 +134,6 @@ public class GetdownApplet extends JApplet
         // if our getdown.txt file does not exist, auto-create it
         File gdfile = new File(appDir, "getdown.txt");
         if (!gdfile.exists()) {
-            String appbase = getParameter("appbase");
             if (StringUtil.isBlank(appbase)) {
                 Log.warning("Missing 'appbase' cannot auto-create " +
                             "application directory.");
@@ -96,7 +147,6 @@ public class GetdownApplet extends JApplet
         }
 
         // if a background image was specified, grabbit
-        String imgpath = getParameter("bgimage");
         try {
             if (!StringUtil.isBlank(imgpath)) {
                 _bgimage = getImage(new URL(getDocumentBase(), imgpath));
@@ -156,6 +206,10 @@ public class GetdownApplet extends JApplet
     @Override // documentation inherited
     public void start ()
     {
+        if (!_safe) {
+            return;
+        }
+
         try {
             _getdown.start();
         } catch (Exception e) {
@@ -188,4 +242,10 @@ public class GetdownApplet extends JApplet
 
     protected Getdown _getdown;
     protected Image _bgimage;
+
+    /**
+     * Getdown will refuse to initialize if the jar is signed but the
+     * parameters are not validated to prevent malicious code from being run.
+     */
+    protected boolean _safe = false;
 }
diff --git a/src/java/com/threerings/getdown/launcher/TorrentDownloader.java b/src/java/com/threerings/getdown/launcher/TorrentDownloader.java
index 25a45e5..dcb6cc4 100644
--- a/src/java/com/threerings/getdown/launcher/TorrentDownloader.java
+++ b/src/java/com/threerings/getdown/launcher/TorrentDownloader.java
@@ -83,14 +83,15 @@ public class TorrentDownloader extends Downloader
         Snark snark = _torrentmap.get(rsrc);
         SnarkShutdown snarkStopper = _stoppermap.get(rsrc);
         snark.collectPieces();
+        // Override the start time, since Snark allocates storage prior to
+        // doing any downloading
+        _start = System.currentTimeMillis();
         while (_currentSize != snark.meta.getTotalLength()) {
             long now = System.currentTimeMillis();
             if ((now - _lastUpdate) >= UPDATE_DELAY) {
                 _currentSize = snark.coordinator.getDownloaded();
                 if ((_currentSize < SIZE_THRESHOLD &&
-                        (now - _start) >= TIME_THRESHOLD) ||
-                        (_currentSize == 0 &&
-                            (now - _start) >= TIME_THRESHOLD / 4)) {
+                        (now - _start) >= TIME_THRESHOLD)) {
                     Log.info("Torrenting too slow, falling back to HTTP.");
                     // The download isn't going as planned, abort;
                     snarkStopper.run();
diff --git a/src/java/com/threerings/getdown/tools/AppletParamSigner.java b/src/java/com/threerings/getdown/tools/AppletParamSigner.java
new file mode 100644
index 0000000..202fe47
--- /dev/null
+++ b/src/java/com/threerings/getdown/tools/AppletParamSigner.java
@@ -0,0 +1,59 @@
+package com.threerings.getdown.tools;
+
+import java.io.BufferedInputStream;
+import java.io.FileInputStream;
+import java.security.KeyStore;
+import java.security.PrivateKey;
+import java.security.Signature;
+
+import org.apache.commons.codec.binary.Base64;
+
+/**
+ * Produces a signed hash of the appbase, appname, and image path to ensure
+ * that signed copies of Getdown are not hijacked to run malicious code.
+ */
+public class AppletParamSigner
+{
+    public static void main (String[] args)
+    {
+        try {
+            if (args.length != 7) {
+                System.err.println(
+                    "AppletParamSigner keystore storepass alias keypass " +
+                    "appbase appname imgpath"
+                );
+                System.exit(255);
+            }
+            String keystore = args[0];
+            String storepass = args[1];
+            String alias = args[2];
+            String keypass = args[3];
+            String appbase = args[4];
+            String appname = args[5];
+            String imgpath = args[6];
+            String params = appbase + appname + imgpath;
+
+            KeyStore store = KeyStore.getInstance("JKS");
+            store.load(new BufferedInputStream(new FileInputStream(keystore)),
+                storepass.toCharArray());
+            PrivateKey key = (PrivateKey)store.getKey(alias,
+                keypass.toCharArray());
+            Signature sig = Signature.getInstance("SHA1withRSA");
+            sig.initSign(key);
+            sig.update(params.getBytes());
+            String signed = new String(Base64.encodeBase64(sig.sign()));
+            System.out.println(
+                "<param name=\"appbase\" value=\"" + appbase + "\" />");
+            System.out.println(
+                "<param name=\"appname\" value=\"" + appname + "\" />");
+            System.out.println(
+                "<param name=\"bgimage\" value=\"" + imgpath + "\" />");
+            System.out.println(
+                "<param name=\"signature\" value=\"" + signed + "\" />");
+        } catch (Exception e) {
+            System.err.println("Failed to produce signature.");
+            e.printStackTrace();
+        }
+    }
+
+}