A Trojan-PWS is very similar to a Trojan-Spy, but is geared mainly towards stealing account log-in details, including passwords (the PWS stands for password stealer). In addition, some Trojan-PWSs may also include spying and data-stealing routines.
Attackers often distribute trojan-PWSes as part of the payload of another harmful program, such as a trojan-dropper, which silently drops and installs the trojan-spy on a device.
They may also be distributed as disguised files attached to emails. In these cases, the attackers rely on social engineering to trick users into opening the attached files, which then silently installs the trojan-PWSes.
Some trojans (particularly on the Android platform) are actually copies of legitimate apps that have been repackaged or trojanized to include harmful components. These are often distributed using the same (or very similar) names and designs as popular programs, to increase the chances that users will mistake the trojan for the legitimate app and install it instead.
To perform its password-stealing routine, a Trojan-PWS will usually drop a keylogging component. Such components stays active in Windows memory and starts keylogging (recording keystrokes) when a user is asked to input a log-in ID and a password.
Stolen log-ins and passwords can allow an attacker to read a user's email on public and corporate mail servers, as well as giving access to more sensitive material, such as online banking accounts.
As of March 2010, the former naming convention 'Trojan-PSW' has been updated to 'Trojan-PWS' to make identification easier for users and to ensure naming practices are in line with current industry standards.