I started this job late last year, and was naturally very friendly with all my coworkers including this particular male colleague (call him X). We use a popular instant messaging system for communicating at work, for which I was advised to create a new work account for and add all colleagues to facilitate contact. I did, and used a generic password that we all use for our computer logins.
About a month into my employment, a female colleague of mine cautioned me that X has basically made attempts to hit on all the women at work, including very inappropriate attempts, and doesn't take no for an answer. During that time X had been chatting with me over workplace messaging system and I have kept contact to a polite minimum. Then one day X, over IM, creates this fictional story that all our IM communication and internet activity is monitored. I was obviously shocked, and he then gave me his phone number and asked for mine to talk about it outside of work. I, then, recognised that this was an attempt to get my number and refused to give it to him. A week or so later, he sent me an IM saying he owes me an apology as this was all made up. I then completely ceased all non-work related contact with him and stopped responding to his IM messages. He responded by trying to create conversation with me, but only when none of our co-workers were around. I became very uncomfortable and snapped at him several times for refusing to leave me alone. I contemplated reporting him for harassment, but didn't think any of what happened constituted workplace harassment so didn't. He, eventually, got the message and stopped IM'ing or talking to me. I was relieved.
However, yesterday, I happened to be checking my work IM's privacy settings and somehow landed on my blocked contacts. Under which, I found another account of his (with his first name and last name) that I had never added or blocked. This obviously means that he got access to my IM or computer account, which isn't hard as I've only used generic passwords for both. I have no idea why he would do that or what he gained from it, and I find it very creepy.
Sorry this is very long, but I thought context might give you an idea as to what action I can now take, if I should take any, and what rights I would have in this situation. Thank you very much in advance.