Forewarned is forearmed, and stuff like that.Simply connecting to the Internet — and doing nothing else — exposes your PC to non-stop, automated break-in attempts by intruders looking to take control of your machine surreptitiously.
While most break-in tries fail, an unprotected PC can get hijacked within minutes of accessing the Internet. Once hijacked, it is likely to get grouped with other compromised PCs to dispense spam, conduct denial-of-service attacks or carry out identity-theft scams.
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Each PC was connected to the Internet via a broadband DSL connection and monitored for two weeks in September. Break-in attempts began immediately and continued at a constant and high level: an average of 341 per hour against the Windows XP machine with no firewall or recent security patches, 339 per hour against the Apple Macintosh and 61 per hour against the Windows Small Business Server. Each was sold without an activated firewall.
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While attempted break-ins never ceased, successful compromises were limited to nine instances on the minimally protected Windows XP computer and a single break-in of the Windows Small Business Server. There were no successful compromises of the Macintosh, the Linspire or the two Windows XPs using firewalls. That pattern was not surprising, as Windows PCs make up 90% of the computers connected to the Internet, and the vast majority of automated attacks are designed to locate and exploit widely known Windows security weaknesses.
USA Today