Grammatical gender in German isn't really arbitrary; it is usually determined by the word's suffix (though there are plenty of exceptions). For example, computer is grammatically male in German, like most words ending in -er.

Things can get complicated if a loanword does not have a suffix that exists in German (or is reasonably close to an existing suffix). In this case, you may get regional variations (that can be pretty random) or the grammatical gender of the German translation of the loanword may be adopted instead.

Examples of feminine loanwords: E-Mail (because the word "Post" in German is feminine), URL (because words ending in -el tend to be feminine).