Some spammers search the internet for unprotected computers they can control and use anonymously to send spam, turning them into a robot network, known as a "botnet." Also known as a "zombie army," a botnet is made up of many thousands of home computers sending emails by the millions. Most spam is sent remotely this way; millions of home computers are part of botnets.
Spammers scan the internet to find computers that aren't protected by security software, and then install bad software – known as "malware" – through those "open doors." That's one reason why up-to-date security software is critical.
Malware may be hidden in free software applications. It can be appealing to download free software like games, file-sharing programs, customized toolbars, and the like. But sometimes just visiting a website or downloading files may cause a "drive-by download," which could turn your computer into a "bot."
Another way spammers take over your computer is by sending you an email with attachments, links or images which, if you click on or open them, install hidden software. Be cautious about opening any attachments or downloading files from emails you receive. Don't open an email attachment — even if it looks like it's from a friend or coworker — unless you are expecting it or know what it contains. If you send an email with an attached file, include a text message explaining what it is.
