If a Kaspersky Lab product installed on your computer displays the error "Activation error: Untrusted server certificate" or "Activation error: 0x00000025", then in order to resolve the problem, perform the following actions:
1. Check the system date
See if the system date is set correctly.
2. Check your Internet connection via Internet Explorer
Сheck if you have the Internet access. In order to do so, launch the browser Internet Explorer and open the site www.kaspersky.com.
3. Configure your Firewall
If Firewall is installed on your computer, make sure that an allowing rule is created for the process avp.exe in the Firewall settings.
Firewall secures your computer protection on local networks and Internet. Firewall is a program which monitors data transferred via Internet or local networks. According to the Firewall settings, it blocks or allows data transferring.
4. Try to activate later
If the recommendations described above did not help to resolve the problem, try to activate later (in about an hour).
5. Contact Kaspersky Lab Technical Support
If the error keeps repeating create a request to Kaspersky Lab Technical Support via the My Kaspersky Account service. Describe you problem in all details.