There are many problems with Google's services lately. After Google Groups had some temporary glitches, some people report that Google switches them to random accounts.
Jvy Loh writes on his blog about the incidents:
"It started off when I was using gg docs and after closing 1 of my docs, I was returned to my 'doc home', however, someone else's email was reflected at the top instead of mine. It disappeared soon after before I could catch what was going on. (...) Lately, the google problem came up again. Nearly everytime I boot up my computer, and login to google toolbar or gmail, I began to notice that when I went further to click on other google services, e.g. gg reader, very often I went into someone else's reader. Not just their email id replacing mine at the top, it was literally someone's reader. I could read their feeds and so on. (...) The MOST SERIOUS thing so far is that you can accidentally made changes to other user's account while you think you are modifying your own. I realized that when I was making changes/adding items, like adding a bookmark, adding a feed into my reader, and adding notes to my notebook, adding gg gadgets to my igoogle, rearranging my igoogle layout, the changes all went to the other party, not mine, and hey this is scary!"
He also mentions that the users seem "to be originating from the same city, which is Singapore, and I suspect some of them are students, by browsing through the gg reader feeds presented to me, and supposingly 'my bookmarks'. (...) Not only did it appear in Singapore, those users seem to be from the same organization, which are local universities, 1 from NTU, and some may be from NUS, and fyi the 2 top universities in Singapore are located in the west of Singapore, and I am in the north-west, which is pretty near to each other."
Other Google user complains over at Google Groups: "Whenever I use Google Reader, I would 'cross-over' to another user's account."
And another one: "I've been login to other users today, seeing their feeds instead of mine. I login to gmail and google reader. While reading the feeds halfway I would see my feeds change into other user's [feeds], my account will also change to other google user account."
Other report from a regular reader of this blog: "While I was reading posts in Google Reader today, my account was switched to someone else's account. The account name on the upper right corner changed and I could see all his or her subscriptions in my Google Reader. I closed the Reader and open it again. Nice! I could read another person's subscriptions. I tried iGoogle and it was also changed."
It seems that this isn't an isolated incident and it may have something to do with Google cookies and Google Reader, but it's not very clear. If you had similar problems or you know what causes them, please let us know.
Update. Matt Cutts, from Google, posted this: "Given that most of these reports are coming from a single area (Singapore), it sounds like an ISP isn't handling their connections correctly. We've certainly seen ISPs mess up their proxies before. I'll still ask about this though."
Update 2. Jvy Loh writes: "Since last Saturday [July 22] after Google Reader was patched (need confirmation from Google whether the Google Reader or local ISP proxy/cache played a bigger part in this security problem), I have not noticed any more security glitches. Two other Singapore users who contacted me also reported no more security issues since then. So, we have enough reasons to think that the security issues related to what I have reported have been eliminated."