Some contacts not appearing online

Hi to you all, this problem has driving me crazy for several months now, I'll try to be short with this:

By chance 3 contacts from my friends list stopped getting online almost simultaneously; I already checked and none of them have deleted me nor blocked me, I just haven't had any contact with them since then and I'm desperate as to know what is happening.

Also:

Before this triple problem the same happened to me with one of my contacts (which is actually one of this 3 people): I stopped seeing her online and therefore talking to her for like 2-3 months and eventually one day she got online, I told him what had happened and she didn't know what was I saying; she told me that she had been getting online as always and that all this time she could actually see me online, she even thought I didn't want to talk to her, but it's just that I couldn't see her online!; well, the same is happening to me again now but with 2 more contacts.

Like I said, deleted/blocked is not an option, what else can it be happening?

By the way, excellent forum, you have helped me a lot in past occasions.

Try to look into the options and have it notify you when someone comes online, or maybe you have malware or a bot logging onto your account without your knowledge.

Snow(ConFed) said:

Try to look into the options and have it notify you when someone comes online, or maybe you have malware or a bot logging onto your account without your knowledge.

Click to expand...

Yes, that's already marked, thanks for the recommendation anyways.
About the malware/bot thing, what software do you recommend me to you use for such thing?

I would say MalwareBytes.

For full Security protection, use Microsoft Security Essentials and Windows Firewall. It's great for speed, security, and protection, along with Malware bytes. It's all free.

Third link may solve your problem.

LINKS:
1 Malwarebytes.org
2 http://www.microsoft.com/security_essentials/
3 http://forum.msgstuff.com/archive/index.php/thread-446.html

Thanks a bunch, both programs are really nice, made me get rid of old Ad-Aware. Regarding third link, well, I just did all the steps they recommended there, I'll post later the results

You're welcome :D

If there's anything else you need help with, don't hesitate to ask.

Unfortunately, it seems what I did didn't work as the problem is still there