Obviously Deezer have a weak content protection. For whatever reason my Internet Explorer 7 caches their music. And there is a Dysnomia Project that created a flash plug-in pretending to be Deezer flash plug-in. Besides computer geeks can easily analyze post request to deezer server so that it will be easy to download music from Deezer.

But all the tricks violate the ToS of Deezer.com so you shouldn't use them!

As for Deezer, they should probably use proprietory music protocols and/or formats. Otherwise not only direct sound recording software will be used to get music from their service.

Besides they should state clearly on every page that recording music from the service violates their ToS.