The messages are short ("a must see LINK", "young girls are waiting LINK") and are spewed from bot and compromised accounts. Both contain links to a .tk domain.
Following the link in the first message lands victims on a page (detectoptimizersupervision(dot)info) serving the bogus Windows Antivirus 2012, which is currently detected by only 3 of the 42 AV solutions used by VirusTotal:
The offered variant is changed every three to six hours.
The second one redirects users to a website where the Blackhole exploit kit drops a first rogue AV then redirects to another page offering another one named Windows Antivirus Patch.
Twitter has been notified of the campaigns and has hopefully been taking the messages down, but just in case, users are advised to be careful and avoid links to .tk URLs.