The Center for Democracy and Technology has in recent weeks contacted 10 Fortune 500 businesses that have advertised with companies engaged shady dealings, including the use of spyware, reports MediaPost. The group hopes the firms will implement guidelines that encourage advertising transparency and discourage the use of spyware or adware installed without user permission. The initiative is still in its early stages, and a list of 25 Fortune 500 companies has been drawn up by adware/spyware consultant Ben Edelman. Some of the companies contacted by the Center have standards in place that prohibit spyware - but online advertising's string of middlemen sometimes obscure violations of those guidelines.