Problems with this Site

Hi Guys, I have had numerous problems on this site lately which makes me think that hackers have infiltrated my system. I dont know alot about computers and my comment may sound really stupid. I have a imac and while posting the other day my post came up with someone elses photo and name. I apologised cos I have no idea how it happened. I reported it immediately to the administrator but have not heard back. This site is very unstable on my imac and it doesnt matter if I use safari or internet explorer. actually explorer is worse Some really weird things have been happening. What I want to know is, can someone access and use your computer and you dont know it and post on this forum or are they accessing all my data on my computer. Is there an explanation anyone.