Miguel,
the solution is relative simple (in this order, follow the steps):
1 - make sure that you have a proftpd file in /usr/sbin/
2 - make sure that the /usr/sbin/proftpd is NOT the one installed by the atomic upgrade (i.e. installed by yum upgrade psa-proftpd). For this, check the version with command: proftpd -v
3 - verify that version is some of this:
a) version 1.3.1 or smaller (without hotfixes),
b) 1.3.2e (with or without hotfix, due to some unfortunate naming by Parallels in the hotfix) or
c) 1.3.3c (when using an official release from the proftpd community).
4 - if version is not one of the above, then:
a) first issue the command: mv /usr/sbin/proftpd /usr/sbin/proftpd.art
b) download and compile a 1.3.3c release from proftpd community (compilation just by issuing the commands, 1) ./configure and 2) make install),
c) issue the command: cp [compilation directory]/proftpd to /usr/sbin/proftpd
5 - to be sure, issue the command: service xinetd restart
6 - go to /usr/local/psa/admin/sbin and run ./autoinstaller
7 - verify that it updates the hotfix when downloading and installing the updates
8 - to be sure, issue the command: proftpd -v
9 - verify that the proftpd version is 1.3.2e
NOTE: the version from step 9 is the psa-proftpd version number and not the proftpd version that is vulnerable. In fact, the psa-proftpd 1.3.2e is actually a compiled version of proftpd 1.3.3c, which is secure. No worries!!!
(Parallels made an unfortunate and confusing naming decision in the hotfix)
10 - final step: manually delete files installed by atomic upgrade (if required, since they are on the system without any function, so no worries here if they are left).
This should work for all forum members that encounter problems related to failures to upgrade to 9.5.3, applying the hotfix or removing "atomic upgrade".
Solution for older versions than 9.5.3:
- run steps 3 to 5
- if necessary or required, make symlinks for the /usr/bin/ftp*** files and link them to the [compilation directory]/ftp*** files (otherwise, issuing commands like ftpwho or ftpcount can yield error messages, due to the fact that the /var/run/proftpd/scoreboard file is of the newer version 1.3.3c)
- APPLY HOTFIX supporting your plesk version LATER, when it is delivered by Paralllels (should not give any problems)
REMARK: solution for versions older than 9.5.3. is a temp fix that also allows you to KEEP OPEN FTP service, WITHOUT being vulnerable to the security leak in older proftpd versions (not to be mistaken with psa-proftpd, the file compiled by Parallels).
Kind regards....