Exemplo ProgressBar

Form1.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Threading;
using System.Windows.Forms;

namespace ProgressBarExemplo
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {            
            for (int i = 1; i <= 100; i++)
            {
                Thread.Sleep(100);
                backgroundWorker1.ReportProgress(i);
            }
        }

        private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            progressBar1.Value = e.ProgressPercentage;
            Text = e.ProgressPercentage.ToString();

            if (progressBar1.Value >= 1 && progressBar1.Value <= 50)
            {
                label1.Text = "Installing Virus";                
            }
            else if (progressBar1.Value > 50 && progressBar1.Value <= 100)
            {
                label1.Text = "Downloading Virus";
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            backgroundWorker1.RunWorkerAsync();
        }
    }
}