During the release of version 2.6.1-rc0, packages were accidentally published into the MongoDB yum and apt repositories such that new and upgrade requests would install the release candidate 2.6.1-rc0 instead of 2.6.0 (stable release).
Users expecting to install, upgrade to, or retain version 2.6.0 may have inadvertently installed version 2.6.1-rc0, which is a release candidate and not recommended for production use. However, we do not expect that accidentally updating to 2.6.1-rc0 will adversely affect your data or operations.
The packages were incorrectly published on April 22, 5:30pm EDT. The issue was resolved on April 23, 11:30AM EDT. Users who attempted to install or upgrade to version 2.6.0 during this time were affected by this issue.
More information for this issue can be found here: https://jira.mongodb.org/browse/SERVER-13691