The official exchange has undergone a minor upgrade. The community has been "hacking" the game a lot since its release, and custom hacks and objects have been released on fansites and forums quite a lot. However, lots and sims using such hacks uploaded to the exchange were packed with such hacks, even if you don't want them. Maxis has now changed the exchange so if any custom hacks not made by Maxis are included, a little warning icon is displayed with the details of the item. On the details page of the package, which lists all the custom content that's included, the CRC and default filename is included in the list. This makes it easier for you to find the hacks and delete them from your Downloads folder. For more about this, see the hack help page that Maxis made for this.