A decade ago, Cato scholars argued that the Justice Department’s antitrust case against Microsoft was a witch hunt instigated at the behest of Microsoft’s competitors. They also warned about the inevitably harmful consequences of the politicization of the technology industry. Once technology firms succeed in hobbling a competitor using antitrust law, other companies are likely to respond in kind, leading to a never-ending stream of antitrust litigation.

That prediction has been borne out in spades, as Microsoft, once a principled critic of antitrust law, has discovered the joys of using antitrust as a competitive weapon. This week we learn that Microsoft has enlisted the assistance of a public relations firm to build support for blocking Google’s acquisition of DoubleClick on antitrust grounds. Never mind that there are dozens of firms in the highly competitive online advertising industry, including aQuantive, a company Microsoft snapped up for $6 billion back in May.

Of course, Google’s hands aren’t clean either. In June, we learned that Google has asked the Justice Department to investigate Microsoft for “bundling” a search functionality with its operating system, despite the fact that desktop search has been a standard feature of operating systems for decades.

Unfortunately, we seem to have opened a Pandora’s Box that will be difficult to close. It’s a shame that Microsoft has backed down from its former, principled stance on antitrust, but it’s hardly surprising. Filing frivolous antitrust complaints is now just a part of doing business in the software industry. That’s great for antitrust lawyers, but it’s hard to see how anyone else benefits.