I bought a security plus license from ebay and upgraded my ASA5505 base license to security plus license:
Licensed features for this platform:
Maximum Physical Interfaces : 8
VLANs : 20, DMZ Unrestricted
Inside Hosts : 10
Failover : Active/Standby
VPN-DES : Enabled
VPN-3DES-AES : Enabled
SSL VPN Peers : 2
Total VPN Peers : 25
Dual ISPs : Enabled
VLAN Trunk Ports : 8
Shared License : Disabled
AnyConnect for Mobile : Disabled
AnyConnect for Linksys phone : Disabled
AnyConnect Essentials : Disabled
Advanced Endpoint Assessment : Disabled
UC Phone Proxy Sessions : 2
Total UC Proxy Sessions : 2
Botnet Traffic Filter : Disabled
Step 1: Registration
Go to http://www.cisco.com/go/license, you need a CCO account to login, after login you will have to enter the product authorization key which comes with your license you have purchased.
You will need to enter your ASA5505 serial number as well:
Use show version or show activation-key command to check your serial number.
Within an hour Cisco will send you a mail with the activation key.
Step 2: Install the license
activation-key <the key you received from cisco>
After you have entered the activation key you must reload your ASA5505 to take effect.