Many people are using the Shareware version of Winzip to create or open .zip or other archives. As Winzip is also a commercial product, the makers want to convinve the users of the shareware version to upgrade to the paid product. So, when you start Winzip, they show a message telling your to purchase. The longer you use the shareware version, the longer it takes before you can click the message away. This message is called a Nag-Screen, for obvious reasons.

Luckily for those who do not want top be nagged, there are alternatives to Winzip. For example 7Zip.