The Protection Trio
Most antivirus software applications will not co-exist harmoniously on one machine, as many of them will cancel each other out, leaving glaring gaps for malware to seep through. A similar scenario will be created if a user has two firewalls installed on the same computer. However, this problem does not extend to applications performing different security jobs.
It is vital to have the troika of security applications: a good antivirus application, an antispyware program and a firewall.
Antivirus applications periodically scan the computer in question for malware. They can also be used to scan downloads for viruses. Mostly these applications are geared towards viruses, although they sometimes can catch worms, Trojans and other malware. However, it is best not to rely on just an antivirus for detecting malware.
Antispyware picks up on malware hidden deep within freeware, usually masquerading as something else. Unlike the other two kinds of security applications, two different programs can co-exist on the same system. In fact, this is sometimes recommended as one antispyware application is unlikely to catch all the threats currently circulating.
Firewalls are necessary, even though dealing with their constant alerts initially can be somewhat annoying. They detect any incoming connections to the computer, as well outgoing ones. A user can then set which connections are trusted, and accordingly the firewall is configured. Incoming threats are fairly straightforward, as those are direct attacks; it is the outgoing connections that are often overlooked. If a Trojan has slipped in, through the defences, it will attempt to connect to an external computer. These connections are hidden from the user, so will go unnoticed without a proper firewall.