A TXT record (short for text record) is a type of resource record in DNS used to provide the ability to associate some arbitrary and unformatted text with a host or other name, such as human readable information about a server, network, data center, and other accounting information. A domain is not limited to having only one text record, any fully qualified domain may potentially have several records. Common uses include defining to verify domain ownership or in setting up Sender Policy Framework, DomainKeys, and DomainKeys Identified Mail records which are used to validate legitimate email sources from a domain. Not everyone knows, but this record has a different and uncommon use 
Let say you have a domain name called yourdomainnamewithtxtrecord.com or yourdomainnamewithtxtrecord.domain.com with an access to edit DNS records such as A, CNAME, MX, TXT etc.
1. Login to your domain admin panel and add this for TXT record:
2. Now you will have to harvest a list of on-line DNS Lookup tools that allow to index their result pages for TXT lookup queries e.g.:
hxxp : / / dnstools.fastnext.com/index.php?fDNSLookup=yourdomainnamewithtxtrecord.com&fDNSServer=&sDNSLookup=TXT
hxxp : / / dnssy.com/lookup.php?q=yourdomainnamewithtxtrecord.com&t=TXT
hxxp: / / whatsmyip.us/dns_txt.php?host=yourdomainnamewithtxtrecord.com
hxxp: / / mxtoolbox.com/SuperTool.aspx?action=txt:yourdomainnamewithtxtrecord.com
hxxps: / /dnssniffer.com/en/dnsreport/yourdomainnamewithtxtrecord.com
hxxp: / / dig-nslookup.nmonitoring.com/dns-dig-nslookup.html?domain=yourdomainnamewithtxtrecord.com&pingsub=1
hxxps: / / network-tools.webwiz.co.uk/dns-records.htm?host=yourdomainnamewithtxtrecord.com&type=TXT&server=&recursion=true
etc etc.
3. Index it and enjoy free backlinks
Let say you have a domain name called yourdomainnamewithtxtrecord.com or yourdomainnamewithtxtrecord.domain.com with an access to edit DNS records such as A, CNAME, MX, TXT etc.
1. Login to your domain admin panel and add this for TXT record:
Code:
BHS1 IN TXT ?< a href=?hxxp :/ / domainname.com? title=?Keyword?>Keyword</a>?
Code:
BHS2 IN TXT ?< img src=?hxxps : / / lh4.googleusercontent.com/-qZCZ-GPC3sc/US_vGXhbTfI/AAAAAAAAAIk/Hf_gPeSQ-Tc/w426-h284/Matt%2BCutts .g i f?>?
Code:
BHS3 IN TXT ?This is an example of DNS link building. This method also works for XSS attacks.?hxxp : / / dnstools.fastnext.com/index.php?fDNSLookup=yourdomainnamewithtxtrecord.com&fDNSServer=&sDNSLookup=TXT
hxxp : / / dnssy.com/lookup.php?q=yourdomainnamewithtxtrecord.com&t=TXT
hxxp: / / whatsmyip.us/dns_txt.php?host=yourdomainnamewithtxtrecord.com
hxxp: / / mxtoolbox.com/SuperTool.aspx?action=txt:yourdomainnamewithtxtrecord.com
hxxps: / /dnssniffer.com/en/dnsreport/yourdomainnamewithtxtrecord.com
hxxp: / / dig-nslookup.nmonitoring.com/dns-dig-nslookup.html?domain=yourdomainnamewithtxtrecord.com&pingsub=1
hxxps: / / network-tools.webwiz.co.uk/dns-records.htm?host=yourdomainnamewithtxtrecord.com&type=TXT&server=&recursion=true
etc etc.
3. Index it and enjoy free backlinks