The Internet is continuously extending to mobile devices. This implies that applications should be tailored to make efficient use of the limited resources of such devices. Mobile agents are a promising solution for this purpose. However, secure protocols are required in order to assure confidentiality and integrity of the data such an agent collects. This paper describes 6 such security protocols presented in the scientific literature. These protocols are analyzed with respect to a series of security requirements that should be satisfied by such protocols. An overview of some published attacks on these protocols and the proposed solutions is also presented.