Strange sounds or music plays from the speakers unexpectedly.A program disappears from the computer even though you did not intentionally remove the program.Note These are common signs of infection। However, these signs may also be caused by hardware or software problems that have nothing to do with a computer virus. Unless you run the Microsoft Malicious Software Removal Tool, and then you install industry-standard, up-to-date antivirus software on your computer, you cannot be certain whether a computer is infected with a computer virus or not.Symptoms of worms and trojan horse viruses in e-mail messages loadTOCNode(2, 'moreinformation'); When a computer virus infects e-mail messages or infects other files on a computer, you may notice the following symptoms: The infected file may make copies of itself. This behavior may use up all the free space on the hard disk.A copy of the infected file may be sent to all the addresses in an e-mail address list.The computer virus may reformat the hard disk. This behavior will delete files and programs.The computer virus may install hidden programs, such as pirated software. This pirated software may then be distributed and sold from the computer.The computer virus may reduce security. This could enable intruders to remotely access the computer or the network.You receive an e-mail message that has a strange attachment. When you open the attachment, dialog boxes appear, or a sudden degradation in system performance occurs.Someone tells you that they have recently received e-mail messages from you that contained attached files that you did not send। The files that are attached to the e-mail messages have extensions such as .exe, .bat, .scr, and .vbs extensions.