a google search will help you with this one
posting links to external sites is against xda rules unless its your own site for non commercial use (ie not gaining money from ads) for downloading files
11. Don’t post with the intention of selling something.
Encouraging members to participate in forum activities on other phone related sites is prohibited.
Off-site downloads are permitted if the site is non-commercial and does not require registration.
Off-site downloads from sites requiring registration are NOT encouraged but may be permitted if the following conditions are met:
A) The site belongs to a member of XDA-Developers with at least 1500 posts and 2 years membership, who actively maintains an XDA-Developers support thread(s) / posts, related to the download.
B) The site is a relatively small, personal website without commercial advertising / links (i.e. not a competitor forum-based site with purposes and aims similar to those of XDA-Developers.com.)
13. Advertising and Income Generation
Commercial advertising, advertising referral links, pay-per-click links and other income generating methods are forbidden. Do not use XDA-Developers as a means to make money.
by posting links to other sites its a form of advertising