To produce more accurate search results, try not to use words like rapidshare, free, retail, unlock, serial, megaupload, new, keygen, warez, version, release, patch, activation, crack, patch, hack, key, full, cracked, download, torrent, license, hacked, password, code.
The word "serial" in warez context means a unique number which identifies the license of the software as being valid. All retail software uses a serial number or key of some form, and the installation often requires the user to enter a valid serial number to proceed. A serial can also be referred to as a "CD Key". When you search for "zoo tycoon 2 full fersion serial" for example, you may find the word "serial" amongst the results. This usually means your warez download includes a serial number.
