It is a fact that software has bugs. These bugs can lead to failures. Especially dependabil-
ity and security failures are a great threat to software users. This thesis introduces four
novel approaches that can be used to automatically harden software at the user’s site.
Automatic hardening removes bugs from already deployed software. All four approaches
are automated, i.e., they require little support from the end-user. However, some sup-
port from the software developer is needed for two of these approaches. The presented
approaches can be grouped into error toleration and bug removal. The two error tol-
eration approaches are focused primarily on fast detection of security errors. When an
error is detected it can be tolerated with well-known existing approaches. The other two
approaches are bug removal approaches. They remove dependability bugs from already
deployed software. We tested all approaches with existing benchmarks and applications,
like the Apache web-server.