What Went Wrong - How Did my System Get Infected with a Virus?

There are a number of warning signs that indicate the presence of a computer virus infection on your computer system. The same symptoms apply to worm infections and Trojans, malicious code often delivered via contaminated email attachments. The major warning sign is a dramatic decrease in your machine's operating speed, especially if you are connected to a network.

Look for strange operating behavior such as flashing drive or modem lights, corrupted or lost files (especially Word documents and Excel spreadsheets), or unusual program messages (for instance messages that say your files are not in the correct format.) Sometimes programs are disabled and will not open or new icons appear on your desktop. Your speakers my play strange sounds or your monitor's display may be disrupted.

Frequent and unexplained systems crashes are common symptoms of virus infection. Sometimes the system will "han" on start-up or will take an unusually long time to start. You may receive "out of memory" messages or be unable to install new programs. But how does a virus infect your computer in the first place?

How do Computers become Infected by Viruses?

The simple answer to "how do computer viruses infect your computer" is that you have most probably been tricked into doing something that you shouldn't have done, thus allowing the virus to be activated and to propagate. Some of the worst virus and worm infections are attributed to email messages.

The vast bulk of viruses are distributed as attachments to trick email messages. The best piece of advice anyone can follow to protect themselves from computer viruses is, do not open attachments - especially those with the file extensions .vbs or .exe. If you receive a message with an attachment, even from someone you know, send an email asking what the attachment is about and even if they actually sent it.

Many viruses, once activated, send themselves to every email address in the contact list of the infected machine. The virus is designed to appear to be sending benign or useful material or programs. Be suspicious! If you are sending an attachment, clearly state in your message what you are sending (format and content) and expect the same courtesy and caution from your correspondents.

Continue to : When a Computer is Affected by Worm Infections