First things first: I'm not a lawyer.
Depending on the licence you use, these companies may be free to branch your product into either a closed-source project or another open-source competitor (perhaps so they can steer the development). It's always a risk (and a benefit) of using free/open-source licences.
However, if you have reason to suspect that your project is being used outside its licence agreement (by any company, not just Google or Microsoft), you'd do best in not contacting your average lawyer. There are organizations that are passionate about helping you battle in court, such as the Free Software Foundation (Europe, US, and many places). A recent example is the FSF taking Cisco to court, accused of violating the GPL licence.
In summary, to adress your question: yes it is possible. And yes, it has happened before.
Microsoft has previously been accused of "stealing" code from projects on CodePlex and use in their products. I recall that they took parts from the ImageMaster project, used for burning DVDs and used in their own DVD tool [source].
Law is tricky, but I hope I could provide an insight. Cheers!