Trojan horse viruses can infect your PC and steal sensitive information such as user credentials for online access to financial websites. These viruses infect computers when users visit websites that host a malicious code. Once on a user's computer, the virus sits unnoticed until the user logs on to financial websites which are being monitored by the malicious software. It then captures log-in and password information and sends it to a server run by the attackers. It is therefore very important that end users consistently maintain updated virus and anti-spy ware software and download all security patches for their operating system on a regular basis.