under the guise that/under the guise of
Phishing e-mails try to extract valuable information from you so they can rob you under the guise of protecting your online security. They are disguising their theft as protection. There are other related phrases, mostly ending in “that,” such as “under the pretext that” and “with the excuse that”; but “under the guise” requires “of,” usually followed by a gerund ending in “-ing.”
Note for this coming Sunday, if you are in the Seattle area: Paul Brians will be at Eagle Harbor Books at 3 p.m.