Generic PWS is a keylogger trojan, designed to steal passwords and hack users. Specific indications may vary between different password stealing trojan, but typically the trojan will hook system startup via a Registry key, or a modification to WIN.INI or SYSTEM.INI.
Methods of Infection
The trojan may be received from any of many sources. For example via email, IRC, P2P file-sharing network, newsgroup or download.