Hotbar is SOMETIMES the cause of a buffe overrun but it is also quite common from SPYWARE and third party plugins, such as streaming video and ad delivery programs.
Download a copy of Lavasoft's ADAWAER it will check your PC for all spyware. I've seen said "clean" machines turn up with over 75 applications running that spy in the background and send stats to a database for demographic marketing, thus a new influx of SPAM.
You can download ADAWARE for FREE at http://www.lavasoft.nu
If you DO run HOTBAR, it's usually not too buggy, but you can disable it by right clicking on the IE toolbar and unchecking HOTBAR, (if it's even installed).
It is always a good idea to run adaware scans every now and then to stop the stupid little bugs, hangs and slowdowns due to spyware.