According to Proftpd’s website:
The ProFTPD Project team is sorry to announce that the Project’s main FTP server, as well as all of the mirror servers, have carried compromised versions of the ProFTPD 1.3.3c source code, from the November 28 2010 to December 2 2010. All users who run versions of ProFTPD which have been downloaded and compiled in this time window are strongly advised to check their systems for security compromises and install unmodified versions of ProFTPD.
Anyone running a dedicated server or anyone responsible for updating software on dedicated servers, please read and upgrade accordingly.
This just shows how focused hackers are at attacking whatever they can. Please follow their suggestion:
To verify the integrity of your source files, use the PGP signatures which can be found here as well as on the FTP servers.