Noninterference is typically used as a baseline security policy to formalize confidentiality of secret information manipulated by a program. In contrast to static checking of noninterference, this paper considers dynamic, au\-to\-maton-based, monitoring of information flow for a single execution of a concurrent program. The monitoring mechanism is based on a combination of dynamic and static analyses. During program execution, abstractions of program events are sent to the automaton, which uses the abstractions to track information flows and to control the execution by forbidding or editing dangerous actions. All monitored executions are proved to be noninterfering (soundness) and executions of programs that are well-typed in a security type system similar to the one of Smith and Volpano~\cite{Smith:Volpano:MultiThreaded} are proved to be unaltered by the monitor (partial transparency).