Most IT departments in corporations use firewall software that can tell by user what sites they visit and how much data is downloaded from the site. From having viewed logs, internet misusage pops out in a heartbeat. They're not likely to view what you're posting unless they have a packet sniffer on there. Highly unlikelly since that is a lot of work. In any case, be sure to clear you cookies and such every day. Or even a few times a day.