Wiktionary
n. 1 (context computing slang derogatory English) An incompetent computer user. 2 (context computing slang derogatory English) A user (especially in IRC) who disobeys the rules of the servers that he or she is using and usually resorts to disruptive or offensive behavior/behaviour.
Wikipedia
In Internet slang, a luser (sometimes expanded to local user; also luzer or luzzer) is a painfully annoying, stupid, or irritating computer user. The word is a blend of "loser" and "user". Among hackers, the word luser takes on a broad meaning, referring to any normal user (in other words, not a " guru"), with the implication the person is also a loser. The term is interchangeable with the hacker term lamer.
It can also signify a layman with only user account privileges, as opposed to a power user or administrator, who has knowledge of, and access to, superuser accounts; for example, an end luser who cannot be trusted with a root account for system administration. This term is popular with technical support staff who have to deal with lusers as part of their job, often metaphorically employing a LART (Luser Attitude Readjustment Tool, also known as a clue-by-four, cluestick, or cluebat), meaning turning off the user's access to computer resources and the like.
Usage examples of "luser".
One of the sysadmins at Southwest Cyberport told me that almost every day some luser email bombs one of their customers.
And if you start IRC warrioring and get K:lined off the system, just think about that purple nose and black eye you could get when all the other IRC dudes at your ISP or school find out who was the luser who got everyone banned.
You know, those Windows 95 for lusers programs that run from a few mouse clicks?
I will give you the opportunity to gain what you wish and perhaps save a few lives in the process, I have a fully operational six millimetre luser rifle here, and plenty of charges, but I don't see anything worth fighting over.