Microsoft has just been given a monster of a warning about its $26 billion deal for LinkedIn. The software giant’s June swoop for the professional social-networking site already looked pricey. The fate of an erstwhile competitor offers a cautionary tale of how bad it could get. Job-listing board Monster Worldwide was once worth some $8 billion until LinkedIn crushed it. On Tuesday it sold to a Dutch rival for $429 million – and that includes debt. A similar chimera could be lurking in Redmond. Founded in 1994, the same year as Yahoo, Monster.com quickly overhauled the habits of how people searched for jobs. In the process, the ease of hunting on a computer rather than combing through the help-wanted sections of dailies, highlighter in hand, drained the newspaper industry of a vital source of revenue. In 2000, newspapers accounted for some $9 billion in recruitment advertising spending. By 2011 it had dwindled to less than $1 billion.