Actually, there are no Illinois opinions on the ethics of cloud computing.
At least it doesn’t have any formal opinions. However, ISBA Ethics Opinion 10-01 (2009) held that use of an off-site network administrator would not violate the Illinois Rules of Professional Conduct as long as reasonable efforts are made to protect client confidentiality.
Given analogous facts to use of a third-party cloud computing service, such as Online Legal Software, it is reasonable to think Illinois would adopt the same logic as to cloud-computing (which is also in fact the universal position of all the states that have considered the subject)
Should Illinois come out with an opinion directly on the subject, we’ll let you know.