Thanks David, I am changing the heading which you have indicated as false.

I am not using any other firewall other than the Windows 7 firewall.

I have read your reply. But what do think that might be the causes of the following issues:

  1. I did not see the svchost.exe processes in my task manager for the last few months. After starting to get the DCOM and LSASS exploit alerts I found a few of them there.

  2. Now I have reinstalled Windows 7 and installed all those softwares that were installed before. But I can not see any svchost.exe process in the task manager and also not getting any exploit alerts.

  3. I was getting those exploit attacks from not only other IPs of my ISP, but also from some IPs of foreign countries.

I made a reference of the my previous Conficker(aka Kido) worm infection just for that because at that time I also got alerts from Avira Premium Security Suite and Kaspersky Internet Security. Most of the time Kaspersky could block the “Buffer Overflow Exploit” attack but sometimes the worm could penetrate into the system as I often found a arbitrarily named image file in my hard disk that Kaspersky detected as Conficker worm and Kaspersky could kill it sucessfully. Avira could not handle the situation as it was disabled within a few hours after the exploit alert and I could not go to any antivirus website. I didn’t face the problem during using Avira Free Edition that has not any firewall with it. Thus I could realize that both Avast and Kaspersky were deploying their own firewall disabling the default windows firewall and making my pc vulnerable to the worm.

As I am now using Avast 6 Free Edition obviously there is not any issue with the firewall and I am also not matching it with the previous Conficker worm issue. My point is that during Conficker worm attack I used to get buffer overflow exploit alerts by Avira and Kaspersky, sometimes the worm could penetrate into my system and both of them also detected the worm but they either totally (Avira) or partially (kaspersky) failed to defend this worm. As I was getting another exploit alert alerts from Avast I was tensed that if the situation go same!