diff --git a/src/mpcCoreKit.ts b/src/mpcCoreKit.ts
index 3cae7ff..01774c2 100644
--- a/src/mpcCoreKit.ts
+++ b/src/mpcCoreKit.ts
@@ -86,6 +86,10 @@ export class Web3AuthMPCCoreKit implements ICoreKit {
 
   public torusSp: TSSTorusServiceProvider | null = null;
 
+  // new user indication
+  // only true during new user sign up, after reinit or rehydration, the flag will be always false
+  public newUser: boolean = false;
+
   private options: Web3AuthOptionsWithDefaults;
 
   private storageLayer: TorusStorageLayer | null = null;
@@ -1093,6 +1097,7 @@ export class Web3AuthMPCCoreKit implements ICoreKit {
 
   // mutation function
   private async handleNewUser(importTssKey?: string, isSfaKey?: boolean) {
+    this.newUser = true;
     await this.atomicSync(async () => {
       // Generate or use hash factor and initialize tkey with it.
       let factorKey: BN;
@@ -1146,6 +1151,7 @@ export class Web3AuthMPCCoreKit implements ICoreKit {
   }
 
   private async handleExistingUser() {
+    this.newUser = false;
     await this.tKey.initialize({ neverInitializeNewKey: true });
     if (this.options.disableHashedFactorKey) {
       return;
@@ -1283,6 +1289,12 @@ export class Web3AuthMPCCoreKit implements ICoreKit {
 
   private async checkIfFactorKeyValid(factorKey: BN): Promise<boolean> {
     this.checkReady();
+    const factorKeyPrivate = factorKeyCurve.keyFromPrivate(factorKey.toBuffer());
+    const factorPubX = factorKeyPrivate.getPublic().getX().toString("hex").padStart(64, "0");
+    const existingFactorEnc = this.tkey.metadata.factorEncs?.[this.tkey.tssTag]?.[factorPubX];
+    if (!existingFactorEnc) {
+      return false;
+    }
     const factorKeyMetadata = await this.tKey?.readMetadata<StringifiedType>(factorKey);
     if (!factorKeyMetadata || factorKeyMetadata.message === "KEY_NOT_FOUND" || factorKeyMetadata.message === "SHARE_DELETED") {
       return false;
@@ -1403,6 +1415,7 @@ export class Web3AuthMPCCoreKit implements ICoreKit {
     this.tkey = null;
     this.torusSp = null;
     this.storageLayer = null;
+    this.newUser = false;
     this.state = { accountIndex: 0 };
   }
 
diff --git a/tests/factors.spec.ts b/tests/factors.spec.ts
index 539e892..659802b 100644
--- a/tests/factors.spec.ts
+++ b/tests/factors.spec.ts
@@ -1,7 +1,7 @@
 import assert from "node:assert";
 import test from "node:test";
 
-import { EllipticPoint, KeyType, Point, secp256k1 } from "@tkey/common-types";
+import { EllipticPoint, getPubKeyPoint, KeyType, Point, secp256k1 } from "@tkey/common-types";
 import { factorKeyCurve } from "@tkey/tss";
 import { tssLib as tssLibDKLS } from "@toruslabs/tss-dkls-lib";
 import { tssLib as tssLibFROST } from "@toruslabs/tss-frost-lib";
@@ -158,7 +158,7 @@ export const FactorManipulationTest = async (testVariable: FactorTestVariable) =
     });
 
     // enable mfa
-
+    let browserFactor: string;
     await t.test("enable MFA", async function () {
       const instance = await newInstance();
       assert.strictEqual(instance.status, COREKIT_STATUS.LOGGED_IN);
@@ -179,7 +179,7 @@ export const FactorManipulationTest = async (testVariable: FactorTestVariable) =
       const instance2 = await newInstance();
       assert.strictEqual(instance2.status, COREKIT_STATUS.REQUIRED_SHARE);
 
-      const browserFactor = await instance2.getDeviceFactor();
+      browserFactor = await instance2.getDeviceFactor();
 
       const factorBN = new BN(recoverFactor, "hex")
 
@@ -210,9 +210,32 @@ export const FactorManipulationTest = async (testVariable: FactorTestVariable) =
       } else {
         await signSecp256k1Data({ coreKitInstance: instance3, msg: "hello world" });
       }
-
     });
 
+    // replace factor
+    await t.test("replace factor", async function () {
+      const instance = await newInstance();
+    
+      const deviceFactorKeyBN = new BN(browserFactor, "hex")
+      await instance.inputFactorKey(deviceFactorKeyBN); 
+      assert.strictEqual(instance.status, COREKIT_STATUS.LOGGED_IN);
+
+      const newFactorkey = await instance.createFactor({ shareType: TssShareType.DEVICE });
+      await instance.inputFactorKey(new BN(newFactorkey, "hex"));
+
+      assert.strictEqual(instance.status, COREKIT_STATUS.LOGGED_IN);
+
+
+      const deviceFactorPub = getPubKeyPoint(deviceFactorKeyBN);
+      await instance.deleteFactor(deviceFactorPub, browserFactor);
+
+      try {
+        await instance.inputFactorKey(deviceFactorKeyBN);
+        throw Error("should not be able to deleted input factor");
+      } catch (e) {
+        assert(e instanceof Error);
+      }
+    });
   });
 };