どのようにアプリの二回包装を防止しますか？

ソース:http://tieba.baidu.com/p/3289026645
http://www.2cto.com/kf/201503/384492.html

public class SecondPackage{
	private final static String TAG = "SecondPackage"
	
	public SecondPackage(Context context){
		// TODO Auto-generated constructor stub
		this.context = context;
	}
	private Context context;
	
	
	/************protect second package*******************/
	private void byte2hex(byte b, StringBuffer buf) {

		char[] hexChars = { '0', '1', '2', '3', '4', '5', '6', '7', '8',

		'9', 'A', 'B', 'C', 'D', 'E', 'F' };

		int high = ((b & 0xf0) >> 4);

		int low = (b & 0x0f);

		buf.append(hexChars[high]);

		buf.append(hexChars[low]);

		}
	/*

	* Converts a byte array to hex string

	*/

	private String toHexString(byte[] block) {

		StringBuffer buf = new StringBuffer();
	
		 
	
		int len = block.length;
	
		 
	
		for (int i = 0; i < len; i++) {
	
				byte2hex(block[i], buf);
			
				if (i < len-1) {
			
				buf.append(":");
		
			}
	
		}
	
		return buf.toString();

	}
	
	public boolean getSignInfo() {
		boolean checkright = false;
		try {
			PackageInfo packageInfo = context.getApplicationContext().getPackageManager().getPackageInfo(
			"com.xxx.xxx", PackageManager.GET_SIGNATURES);
			Signature[] signs = packageInfo.signatures;
			Signature sign = signs[0];
			
			int code = sign.hashCode();
			MessageDigest md = MessageDigest.getInstance("MD5");
			md.update(sign.toByteArray());
			byte[] digest = md.digest();

			String res = toHexString(digest);

			Log.e(TAG, "apk md5:"+res);
			//if (code == xxxxxxxxx) {
			Log.i(TAG, "hashCode:" + code);
			//  MD5  hashcode        MD5  
			if(res.equals("xxxxxxxxxx")
					&& code == yyyyyyyyyy){
				checkright = true;
			}
			
			
			//parseSignature(sign.toByteArray());
		} catch (Exception e) {
			e.printStackTrace();
		}  
		return checkright;
	}
	
	void parseSignature(byte[] signature) {
		try {
			CertificateFactory certFactory = CertificateFactory  
			.getInstance("X.509");
			X509Certificate cert = (X509Certificate) certFactory
			.generateCertificate(new ByteArrayInputStream(signature));
			byte[] buffer = cert.getEncoded();
			System.out.println( "md5: "+ new String(buffer));
		} catch (CertificateException e) {
			e.printStackTrace();
		}
	}
	/***********************************/
	
}

呼び出し時
SecondPackage sePa=new SecondPackage(this)if(sePa.getSignInfo()==false){finish();