A 
web server computer 
system includes a 
virus checker and mechanisms for checking e-mails and their attachments, downloaded files, and web sites for possible viruses. When an e-mail message contains a detected 
virus, the message is discarded, and both the sender and recipient are informed via e-mail that the message contained a 
virus. When an e-mail attachment contains a detected virus, the attachment is deleted, and the e-mail message without the attachment is sent to the web 
client, along with a message explaining that the e-mail message had an attachment that was automatically deleted because it had a virus. When a downloaded file contains a virus, the downloaded file is deleted, and an 
error message is sent to the web 
client to inform the web 
client that the requested file had a virus. When a requested 
web site (i.e., 
Uniform Resource Locator (or URL)) has been labeled as a source for a known virus, a message is sent to the web client stating that a virus may have been downloaded from that URL. In addition, if the requested URL has not been labeled as a source for a known virus, but it contains links that have been so labeled, the 
web page is processed before being sent to the user to identify those potentially dangerous links. In this manner a 
web server can perform virus checking of different types of information real-time as the information is requested by a web client. In addition, a web client may also request that the 
server perform virus checking on a particular drive on the web client. If this case, the 
web server may receive information from the web client drive, scan the information for viruses, and inform the web client whether any viruses were found. In the alternative, the web 
server may download a client virus checker to the web client and cause the client virus checker to be run on the web client. The preferred embodiments thus allow a virus checker on a web 
server to dynamically scan incoming data, and to scan web clients coupled to the web server, thereby eliminating the need for virus checking 
software to be installed on each web client.