It seems that a recent update of Bitdefender Endpoint Security is blocking the 64 bit version of PL/SQL Developer. The solution is to add the PL/SQL Developer installation directory to the exception list in Bitdefender. For example:

C:\Program Files\PLSQL Developer 14
C:\Program Files\PLSQL Developer 13
C:\Program Files\PLSQL Developer 12

We are investigating the issue and will post any updates here...

It seems that PL/SQL Developer 15.0 is not affected by this issue.

Hallo Marco,

I wanted to download the newest Version 15.0.1 2051 (32 bit) and I become Error in Attachment.
Can you check this and korrekt it?

McAfee is indeed one of the virus scanners that have a false positive detection. Grindsoft, VBA32, and Ikarus also have (different) false positives. All other 54 tested virus scanners report it as clean. We cannot really correct this. See also:

https://www.virustotal.com/gui/file/82d61ee76ac0fc84d6b7ac511d7d61ddbac6a1240bec8af1de7be38a0481e42a