The company said yesterday that it will release five publish bulletins for Windows, at least one of which is critical, Microsoft’s highest severity rating. The firm did not say how many vulnerabilities or patches these bulletins will contain.

There will also be one bulletin affecting Office, which will be critical but will not require a restart, one for MSN Messenger, critical, and one for Exchange, which is also critical but will not require a restart.

The big patch day follows a patchless March. The heads-ups come as part of Microsoft’s recently introduced policy of giving administrators advanced warning of their likely Patch Tuesday workload.