check out the sticky http://www.gnutellaforums.com/showthread.php?t=46086

Although the FrostWire web site has changed, the above sticky explains the relationship between FrostWire and LimeWire.

Yes, much of the code is identical. This is legal, and any additions FW makes to the LW code are available for LimeWire to also use.

So -- no worries. Both are legitimate projects.