Marketers are responsible for any unsolicited marketing messages they send which do not comply with data protection rules. Guidance issued by the Information Commissioner's Office (ICO) stresses that the customer who passes a friend's details to the advertiser must confirm that they obtained the friend's consent. Marketers should check the friend is not already on a marketing suppression list and should tell customers that they will tell the friend how their contact details were obtained. If the friend objects having received the message, the marketer must rapidly suppress his contact details.