Do not open file that you received from a stranger

E-mail and instant messaging (IM) can spread viruses and worms if you aren't careful. Most e-mail viruses are spread by people who are tricked into opening an infected file. Never open a file attached to an e-mail or a file that you received while chatting until you scan them with a good virus scanner. If you do not have a good virus scanner, you can scan the file online by online scanners like http://virustotal.com. It is still not safe to open the file that you received from a known person too, the person may not know that he/she has sent an infected file.