Switching to b25 will prevent it from happening again.

As for converting the files, it's possible but just not worth the effort because
they are already encoded at a very low quality on purpose so that any
conversion to a regular format would make it sound crappy. Not only that, but
that DMCA crud made it temporarily illegal for people in the USA.

When you get b25 go into the Setup menu, go to Filters and make sure WMA,
WMP, ASF, M4P and WMV are in the Extensions list on the right side. That will
stop the few stray "protected" files on the real gnutella network from
showing up in your searches.