What's the difference between act (AU) and rule utilitarianism (RU)? What are the strengths and weaknesses of each?

What's the difference between act (AU) and rule utilitarianism (RU)? What are the strengths and weaknesses of each? In the past Utilitarianism was judged on each individual action, after many years pasted then Utilitarianism was judge on the consequences of the truth and a lie. Your consequences are judged on thoughts such as a promise you made or the truth you was told. "The new version of the theory Rule Utilitarianism, which is distinguishing it …

…It is not acceptable to lie, even if in one situation lying would provide happiness to one person without causing detriment to the other. This is because generally lying produces a negatives effects the majority of the time. The weakness of this theory is that it subjects moral actions to a predetermined "ideal social code". RU may defeat the ability of the Utilitarian theory to promote societal happiness by subjecting inflexible rules to moral situations.