Checking the HTTP Referrer header can also help. Some websites have a referrer log which shows which pages link to that site. Referrer spam filtering functionality was added in version 6.5. This is enforced by checking the referrer header of the HTTP request. Precautions should be taken against referrer spam. This raises the problem of referrer spam. Sending no referrer information is not technically spoofing, though sometimes also described as such. When the user is redirected from the data&colon; page, the original referrer is hidden. The format is extended by the Combined Log Format with referrer and user-agent fields. SFX portal enhanced the "Get Firefox" button program, giving users "referrer points" as an incentive. By checking the referrer, the new webpage can see where the request originated. Any other Referrer should be considered suspicious. Funnyordie.com became the top referrer to the government site during this time. The co-ordinator then makes contact with the referrer. Sometimes a "referrer system" is implemented.