Links converted contains _session in URL

[Biology Forums]

Not so often, when I browse my forum, I links have this bit added to them biologyf_smf_smf1_session. I would like to know what might be a probable cause for this and if it has ever happened to anyone?

http://biology-forums.com/index.php​?biologyf_smf_smf1_session=6goevo28​vf18ubqgb5uh6r08b2&topic=332242​.msg916981
http://biology-forums.com/index.php​?biologyf_smf_smf1_session=6gqvo88l​u5fnl1qmj7temt0113&topic=316196​.msg931242
http://biology-forums.com/index.php​?biologyf_smf_smf1_session=6h1lt0g9​le5uofu5qljkqf56h6&action=pubme​d
http://biology-forums.com/index.php​?biologyf_smf_smf1_session=6h6inhm5​6b08n2f4e63ua7rcr4&topic=323734​.msg917662