Ignorance is bliss, it is said. But I realise I cannot afford the pleasure of ignorance if my pc is to be protected from constant advancement of virus writers.
My laptop Acer Extensa 5620Z is run on Windows Vista Home Basic.
It has the default Windows Defender and I have installed two:
1... Free Antivirus - BitDefender Free Edition
2... avast! - Download antivirus software for spyware and virus protection.

A friend knowledgeable in IT matters tells me I must have Trend Micro protection immediately. He says it will scan the pc and tell me how many viruses have infected my pc and also how to be rid of them.

Please tell me (1) if I should uninstall either BitDefender or Avast as both are described as ''anti-virus''. Both seem to run in backgraound and download and install new updates frequently, on their own.
And (2) follow advise of my friend and get Trend Micro too.

I have experienced in the past these ''free scanners'' demand money after the scan, to remove the items they have discovered in the pc. And I cannot afford to make any payment.

Please advise me as am confused and in fear. Thank you.

Your friend is trying to sell you on his preferences. Not to say that there is anything wrong with Trend Micro as I have used their search engine myself on more than one occasion.

use what ever program that you feel comfortable in installing and using. No matter what it is that you use...it will only work so long as you yourself practice safe browsing and computer usage techniques.

You are the first line of defense There is no one size fits all in computer protection/security.

decide what it is you want in a security program.
1) a suite...a full package of protection with auto updating and all that.. But remember that in choosing this avenue then you are relinquishing control of your computer to the security program. There is less customizing with this type of package deal
2) Individual protection packages
a)Free versions ...you must update them
b) paid versions are self updating
In these programs you have a more customizing selection to work with but must take care in selecting compatible programs.

While there may be other reasons for choosing...this breaks it down to its simplest form.

Thank you for the caution --- I appreciate your advise.