There is not one single bit of truth in this statement. You need to stop hot knifing those styrofoam peanuts. And change your banking passwords, i bet you have 9 keylogger trojans all fighting over who gets to drain your account.
Norton and McAfee are pretty good, but they are way too much of a system hog, performance killer. I hate them for that. I use AVG, it ranks fairly high in its detection and non false positive and its free.
New viruses are constantly being tossed into the wild that there is no detection or cure for. AVG has good heuristic scanning. It checks for virus like activity. Problem is, virus writers are coding to specifically bypass most av.
The best removal tool out there is f-secure's online scan tool.
F-Secure Support pages: F-Secure Online Virus Scanner
I use this whenever I suspect a computer has been infected, it gets stuff all the others miss and scans and removes rootkits too. And spyware. f-secure is a leading virus tracker and they sell cures to companys like norton and avg.
In conclusion. Yes, your best defense is proper surfing/DLing habits. but get your self some AV that is not too system hogging and periodically scan your computer with f-secure.
Used to be that viruses were written to damage your computer, now they are made to hide on your system and steal from you. 99% of people with viruses dont even know they have them until its too late. I have had dozens of people bring me computers because they are infected with spyware, only to discover they have had botnets and keylogger trojans hidden away for months on their machines.