Is using pirated software allowed?

Is using pirated software allowed? Please answer with clear evidence supporting your view. Note that I'm not asking about [whether software piracy itself is sinful](https://islam.stackexchange.com/questions/207/where-does-islam-stand-in-internet-piracy) . My question is regarding the actual *using* of software that was obtained from a pirated source, either with or without the end user's knowledge. For example, many of the computer centres here will sell computers with a pirated OS pre-installed, and they will provide discs of the pirated software. Is it *haram* to use these, given that most of the users don't even realize that what they have is pirated software? Must they stop using the software when they actually learn that it was originally pirated?