Refuse all so-called “Internet Security” packages. You definitely need a good-quality antivirus package, but avoid all the other stuff.
The concept of Internet Security packages had its birth at a time when Windows was not a very safe place. Since then, Windows has progressed immensely to Windows 7.
The other stuff they throw in to those packages is really not needed and is unlikely to protect you better than what Win7 already does. Those other “features” will try to prevent built-in Windows features from working and frequently gets things tangled up.
I have been frustrated too many times when trying to problem-solve a system with one of these installed. I found that by removing the Internet Security software, I was able to identify the problem. I theorize that the other stuff (including its own firewall) does such a good job of hiding itself that it hides the clues to what is wrong. Consequently, I refuse to work on a system with one of these installed.
I have 140 client computers that run only Bitdefender antivirus. I run ADWcleaner when ever I log into a client computer. Excellent product and free. Infections are rare, particulary if they are running Windows 7 and using Internet Explorer.
Update: Symantec (Norton) has removed their antivirus product from the market, September 23, 2014. I am currently installing Bitdefender Antivirus Plus 2015, as client Norton Antivirus subscriptions run out.
Avoid those free Internet Service Provider security packages particularly. I have had numerous occasions when I removed one of these and then installed a good Antivirus product. Within minutes, it identified Trojans happily coexisting with their “security” packages.
The worst ones by far are those “free” ones from your Internet service provider that do not have a brand name. The level of protection they provide is substantially lower than Bitdefender.