Klez.H poses a special threat: the worm scans the disks of an infected computer and depending on a set of conditions attaches a file to each infected email it distributes. Klez.H selects this file from the infected computer's disk storage and looks for files with the following extensions:
.txt .htm .html .wab .asp .doc .rtf .xls .jpg .cpp .c .pas .mpg .mpeg .bak .mp3 .pdf
The result being the possible leakage of important confidential information, the consequences of which cannot be foretold. In a similar fashion, near the end of 2001, the Internet-worm SirCam made public classified documents from a score of government institutions representing different countries from around the world. "In contrast to earlier versions, Klez.H does not have the ability to destroy stored data. Instead Klez.H maintains its threat from its ability to, unsanctioned, mail out files from the infected computer,"- commented Eugene Kaspersky, Kaspersky Labs Head of Anti-Virus Research - "Under these conditions Klez.H poses a greater threat to corporate clients for which an information leak can have unpredictable consequences."
The speed at which Klez.H has spread demonstrates that the majority of users have ignored the advice to install the Internet Explorer security patch that will protect a computer from any version of Klez as well as from future modifications of it. In addition users do not regularly update anti-virus program databases. The consequence of this lax behavior is the Klez.H has a good chance to achieve a large-scale epidemic just like another infamous version of this worm - Klez.E, which already for several months has confidently taken first place in the list of most wide-spread viruses.
Considering the high danger of infection from Klez.H, Kaspersky Labs once again strongly recommends users update their Kaspersky Anti-Virus database. For more thorough protection users should install the Internet Explorer security patch found at:
Kaspersky Labs is providing a free utility that will detect and remove all of the most widely spread versions of Klez, including Klez.H. You can download this utility at the following address: ftp://ftp.kaspersky.ru/utils/clrav.com.