I write computer programs such as nutrition software and had no particular interest in antivirus software until my computer was invaded by a malicious software program. Then I wanted to know,

"What is the Best Antivirus Program?"

I found that there are several independent testing labs including ICSA Labs, Virus Bulletin, West Coast Labs, AV-Comparatives, and AV-Test, that provide reliable information on the effectiveness of antivirus software.

AV-Test recently published test results for antivirus software from 29 software companies.  The test was conducted in September 2008. This most recent test, using current computer viruses and malicious software, changed the ranking quite a bit from previous tests. Things can change fast in the battle between virus makers and antivirus software companies.

Trend Micro software fell out of the top ranked programs this time, even though they scored well about 6 months ago. Many well known antivirus programs did not score over 98% detection of malicious software in the September 2008 test by AV-Test.org.  Those that did not make the cut include: Bit Defender, NOd32, Sophos, Trend Micro, ZoneAlarm, McAfee and AVG, the popular free antivirus program.

Of the 29 software companies tested only 9 scored higher than 98% in testing for Malware on Demand. The Top 9 Scores are:
  Antivir 99.8%
  Avast! 99.3%
  AVK 2009 99.8%
  Ikarus 99.5%
  Kaspersky 98.4%
  Norton 2009 98.7%
  TrustPort 99.5%
  WebWasher-GW 99.7%
  F-Secure 2009 99.2%

I also make sure to check the reviews at CNET because they have a very good staff of computer experts on board. CNET has reviewed 7 antivirus products over the last year.  Their rankings are as follows: (The number in parenthesis is CNET editor's rating.)

Norton Antivirus 2009 (4)
Kaspersky Antivirus 2009 (3.5)
Vipre Antivirus (3.5)
NOD32 by Eset (3.5)
AVG Antivrus 8 (3.5)
Trend Micro Internet Security 2009 (3.5)
F-Secure Internet Security (3)

Only Kaspersky Antivirus, and Norton Antivirus scored higher than 98% in the AV-Test.org September ranking and also got a CNET editor's score of greater than 3.

CNET reports that Norton Antivirus 2009 is a much improved product from their programs of previous years.  It does not slow down computer speed as much as it did in the past and also does not slow down boot time much. The company listened to complaints and made big improvements to their program. 

Features	Kaspersky Antivirus	Norton Antivirus
Price	$59.95	$39.99
Virus Definition Updates	Every hour	About every 15 minutes
ICSA Certification	Yes	Yes
Scan files on access	Yes	Yes
Scheduled scanning	Yes	Yes
Scan compressed files	Yes	Yes
Spyware detection	Yes	Yes
Email Protection	Yes	Yes
CNET Editor Rating	3.5	4.0
Operating systems
Windows Vista	Yes	Yes
Free Trial Online	Yes	Yes

Kaspersky also holds the Editor's Choice award from PC World Magazine. Norton Antivirus holds the second place award at PC World.

Symantec made big improvements to Norton Antivirus for 2009.  Their main concern was to improve the program so that it did not slow down the computer at all.  This effort received a lot of press so I decided to download a copy and try it for myself.  Amazingly the boot time is not slowed down noticeably at all when Norton is loaded onto the machine.  And the program runs smoothly and unobtrusively in the backround without freezing up operations to scan files as happens with other software.  I can honestly recommend the new Norton Antivirus 2009.  -Robert