You launch the program, and the next thing you know, something completely unexpected happens—maybe your system is gone or your computer is laughing maniacally at you.
But unless you notice your computer acting oddly before the virus has done its worst damage, you may very well not know you have it until it's too late.
It usually loads itself into your computer system when you run a program to which it has attached itself.
From the computer system, it'll then reproduce itself, much like a biological virus would, by attaching copies of itself to other programs on your hard drive.
The best known bit of advice is this: Never open any attachment unless you know who it's from and why they are sending it.These program codes have gone beyond mere annoyances with the worst kinds disabling your PC, but they have become portals for remotely perpetuating more sinister activity that can clandestinely hack into sites, mount denial of services or steal confidential and personal data for fraudulent financial gain at your expense. Among home PC users, you may think having to reinstall your OS after a virus or malware has brought it down is not really expensive as you lose just a day or two to reinstall your programs and rebuilding files, consider that in a business, you could actually lose millions.Just ask Choice Point when it took a million charge in 2005 after cyber criminals hacked into their systems and stole sensitive data from thousands of customers.Common sense is another good weapon in the fight against viruses.Be wary of opening any email attachments, even from your firends , especially if it has been forwarded to them.They may bring up a message like "Merry Xmas" or melt your display.Most of them though, either start destroying your system or your files immediately or on a date specified by their creators—like the much-publicized Michelangelo virus, which erases important pieces of your system on March 6.What can I do to protect myself from computer viruses and Trojans?These days, practically everyone's online, downloading and exchanging files, and developers are in such a hurry to get their Web sites up or their files out that checking for a nasty bug is more of a courtesy than a requirement.More than 60% of respondents indicated their plans to terminate business relationships with a company that lost the data they entrusted to them.In 2004, rootkits were a relatively obscure form of Trojans meant to infect Unix computers.